diff --git a/.changeset/fix-operation-id-preserve-casing.md b/.changeset/fix-operation-id-preserve-casing.md
new file mode 100644
index 0000000000..18388e1e5d
--- /dev/null
+++ b/.changeset/fix-operation-id-preserve-casing.md
@@ -0,0 +1,12 @@
+---
+"@hey-api/openapi-ts": patch
+"@hey-api/shared": patch
+---
+
+**plugin(@hey-api/typescript)**: preserve acronym casing from `operationId` in operation-derived type names under `case: 'preserve'`
+
+**plugin(zod)**: preserve acronym casing from `operationId` in operation schema names under `case: 'preserve'`
+
+**plugin(valibot)**: preserve acronym casing from `operationId` in operation schema names under `case: 'preserve'`
+
+Consumer-visible output change: under `case: 'preserve'`, operation-derived names (request/response/error types, zod/valibot schemas) that previously lowercased acronym segments (e.g. `describeHTTPRequest` → `describeHttpRequest`) now retain the original casing (`describeHTTPRequest`). Downstream code importing these names directly will need to update.
diff --git a/packages/openapi-ts-tests/main/test/3.1.x.test.ts b/packages/openapi-ts-tests/main/test/3.1.x.test.ts
index 2ee3cacfe5..b5538c9179 100644
--- a/packages/openapi-ts-tests/main/test/3.1.x.test.ts
+++ b/packages/openapi-ts-tests/main/test/3.1.x.test.ts
@@ -132,6 +132,39 @@ describe(`OpenAPI ${version}`, () => {
       }),
       description: 'handles preserved identifier casing',
     },
+    {
+      config: createConfig({
+        input: 'acronym-operationid-preserve.yaml',
+        output: 'acronym-operationid-preserve',
+        plugins: [
+          {
+            case: 'preserve',
+            name: '@hey-api/typescript',
+          },
+        ],
+      }),
+      description: 'preserves acronym casing from operationId when case is preserve',
+    },
+    {
+      config: createConfig({
+        input: 'acronym-operationid-preserve.yaml',
+        output: 'acronym-operationid-preserve-sdk',
+        plugins: [
+          '@hey-api/client-fetch',
+          {
+            case: 'preserve',
+            name: '@hey-api/typescript',
+          },
+          {
+            name: '@hey-api/sdk',
+            operations: {
+              methodName: { casing: 'preserve' },
+            },
+          },
+        ],
+      }),
+      description: 'preserves acronym casing from operationId in SDK method names',
+    },
     {
       config: createConfig({
         input: 'case.yaml',
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/client.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/client.gen.ts
new file mode 100644
index 0000000000..cab3c70195
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/client.gen.ts
@@ -0,0 +1,16 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import { type ClientOptions, type Config, createClient, createConfig } from './client';
+import type { ClientOptions as ClientOptions2 } from './types.gen';
+
+/**
+ * The `createClientConfig()` function will be called on client initialization
+ * and the returned object will become the client's initial configuration.
+ *
+ * You may want to initialize your client this way instead of calling
+ * `setConfig()`. This is useful for example if you're using Next.js
+ * to ensure your client always has the correct values.
+ */
+export type CreateClientConfig<T extends ClientOptions = ClientOptions2> = (override?: Config<ClientOptions & T>) => Config<Required<ClientOptions> & T>;
+
+export const client = createClient(createConfig<ClientOptions2>());
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/client/client.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/client/client.gen.ts
new file mode 100644
index 0000000000..9ec9ad887c
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/client/client.gen.ts
@@ -0,0 +1,298 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import { createSseClient } from '../core/serverSentEvents.gen';
+import type { HttpMethod } from '../core/types.gen';
+import { getValidRequestBody } from '../core/utils.gen';
+import type { Client, Config, RequestOptions, ResolvedRequestOptions } from './types.gen';
+import {
+  buildUrl,
+  createConfig,
+  createInterceptors,
+  getParseAs,
+  mergeConfigs,
+  mergeHeaders,
+  setAuthParams,
+} from './utils.gen';
+
+type ReqInit = Omit<RequestInit, 'body' | 'headers'> & {
+  body?: any;
+  headers: ReturnType<typeof mergeHeaders>;
+};
+
+export const createClient = (config: Config = {}): Client => {
+  let _config = mergeConfigs(createConfig(), config);
+
+  const getConfig = (): Config => ({ ..._config });
+
+  const setConfig = (config: Config): Config => {
+    _config = mergeConfigs(_config, config);
+    return getConfig();
+  };
+
+  const interceptors = createInterceptors<Request, Response, unknown, ResolvedRequestOptions>();
+
+  const beforeRequest = async <
+    TData = unknown,
+    TResponseStyle extends 'data' | 'fields' = 'fields',
+    ThrowOnError extends boolean = boolean,
+    Url extends string = string,
+  >(
+    options: RequestOptions<TData, TResponseStyle, ThrowOnError, Url>,
+  ) => {
+    const opts = {
+      ..._config,
+      ...options,
+      fetch: options.fetch ?? _config.fetch ?? globalThis.fetch,
+      headers: mergeHeaders(_config.headers, options.headers),
+      serializedBody: undefined as string | undefined,
+    };
+
+    if (opts.security) {
+      await setAuthParams({
+        ...opts,
+        security: opts.security,
+      });
+    }
+
+    if (opts.requestValidator) {
+      await opts.requestValidator(opts);
+    }
+
+    if (opts.body !== undefined && opts.bodySerializer) {
+      opts.serializedBody = opts.bodySerializer(opts.body) as string | undefined;
+    }
+
+    // remove Content-Type header if body is empty to avoid sending invalid requests
+    if (opts.body === undefined || opts.serializedBody === '') {
+      opts.headers.delete('Content-Type');
+    }
+
+    const resolvedOpts = opts as typeof opts &
+      ResolvedRequestOptions<TResponseStyle, ThrowOnError, Url>;
+    const url = buildUrl(resolvedOpts);
+
+    return { opts: resolvedOpts, url };
+  };
+
+  const request: Client['request'] = async (options) => {
+    const { opts, url } = await beforeRequest(options);
+    const requestInit: ReqInit = {
+      redirect: 'follow',
+      ...opts,
+      body: getValidRequestBody(opts),
+    };
+
+    let request = new Request(url, requestInit);
+
+    for (const fn of interceptors.request.fns) {
+      if (fn) {
+        request = await fn(request, opts);
+      }
+    }
+
+    // fetch must be assigned here, otherwise it would throw the error:
+    // TypeError: Failed to execute 'fetch' on 'Window': Illegal invocation
+    const _fetch = opts.fetch!;
+    let response: Response;
+
+    try {
+      response = await _fetch(request);
+    } catch (error) {
+      // Handle fetch exceptions (AbortError, network errors, etc.)
+      let finalError = error;
+
+      for (const fn of interceptors.error.fns) {
+        if (fn) {
+          finalError = (await fn(error, undefined as any, request, opts)) as unknown;
+        }
+      }
+
+      finalError = finalError || ({} as unknown);
+
+      if (opts.throwOnError) {
+        throw finalError;
+      }
+
+      // Return error response
+      return opts.responseStyle === 'data'
+        ? undefined
+        : {
+            error: finalError,
+            request,
+            response: undefined as any,
+          };
+    }
+
+    for (const fn of interceptors.response.fns) {
+      if (fn) {
+        response = await fn(response, request, opts);
+      }
+    }
+
+    const result = {
+      request,
+      response,
+    };
+
+    if (response.ok) {
+      const parseAs =
+        (opts.parseAs === 'auto'
+          ? getParseAs(response.headers.get('Content-Type'))
+          : opts.parseAs) ?? 'json';
+
+      if (response.status === 204 || response.headers.get('Content-Length') === '0') {
+        let emptyData: any;
+        switch (parseAs) {
+          case 'arrayBuffer':
+          case 'blob':
+          case 'text':
+            emptyData = await response[parseAs]();
+            break;
+          case 'formData':
+            emptyData = new FormData();
+            break;
+          case 'stream':
+            emptyData = response.body;
+            break;
+          case 'json':
+          default:
+            emptyData = {};
+            break;
+        }
+        return opts.responseStyle === 'data'
+          ? emptyData
+          : {
+              data: emptyData,
+              ...result,
+            };
+      }
+
+      let data: any;
+      switch (parseAs) {
+        case 'arrayBuffer':
+        case 'blob':
+        case 'formData':
+        case 'text':
+          data = await response[parseAs]();
+          break;
+        case 'json': {
+          // Some servers return 200 with no Content-Length and empty body.
+          // response.json() would throw; read as text and parse if non-empty.
+          const text = await response.text();
+          data = text ? JSON.parse(text) : {};
+          break;
+        }
+        case 'stream':
+          return opts.responseStyle === 'data'
+            ? response.body
+            : {
+                data: response.body,
+                ...result,
+              };
+      }
+
+      if (parseAs === 'json') {
+        if (opts.responseValidator) {
+          await opts.responseValidator(data);
+        }
+
+        if (opts.responseTransformer) {
+          data = await opts.responseTransformer(data);
+        }
+      }
+
+      return opts.responseStyle === 'data'
+        ? data
+        : {
+            data,
+            ...result,
+          };
+    }
+
+    const textError = await response.text();
+    let jsonError: unknown;
+
+    try {
+      jsonError = JSON.parse(textError);
+    } catch {
+      // noop
+    }
+
+    const error = jsonError ?? textError;
+    let finalError = error;
+
+    for (const fn of interceptors.error.fns) {
+      if (fn) {
+        finalError = (await fn(error, response, request, opts)) as string;
+      }
+    }
+
+    finalError = finalError || ({} as string);
+
+    if (opts.throwOnError) {
+      throw finalError;
+    }
+
+    // TODO: we probably want to return error and improve types
+    return opts.responseStyle === 'data'
+      ? undefined
+      : {
+          error: finalError,
+          ...result,
+        };
+  };
+
+  const makeMethodFn = (method: Uppercase<HttpMethod>) => (options: RequestOptions) =>
+    request({ ...options, method });
+
+  const makeSseFn = (method: Uppercase<HttpMethod>) => async (options: RequestOptions) => {
+    const { opts, url } = await beforeRequest(options);
+    return createSseClient({
+      ...opts,
+      body: opts.body as BodyInit | null | undefined,
+      headers: opts.headers as unknown as Record<string, string>,
+      method,
+      onRequest: async (url, init) => {
+        let request = new Request(url, init);
+        for (const fn of interceptors.request.fns) {
+          if (fn) {
+            request = await fn(request, opts);
+          }
+        }
+        return request;
+      },
+      serializedBody: getValidRequestBody(opts) as BodyInit | null | undefined,
+      url,
+    });
+  };
+
+  const _buildUrl: Client['buildUrl'] = (options) => buildUrl({ ..._config, ...options });
+
+  return {
+    buildUrl: _buildUrl,
+    connect: makeMethodFn('CONNECT'),
+    delete: makeMethodFn('DELETE'),
+    get: makeMethodFn('GET'),
+    getConfig,
+    head: makeMethodFn('HEAD'),
+    interceptors,
+    options: makeMethodFn('OPTIONS'),
+    patch: makeMethodFn('PATCH'),
+    post: makeMethodFn('POST'),
+    put: makeMethodFn('PUT'),
+    request,
+    setConfig,
+    sse: {
+      connect: makeSseFn('CONNECT'),
+      delete: makeSseFn('DELETE'),
+      get: makeSseFn('GET'),
+      head: makeSseFn('HEAD'),
+      options: makeSseFn('OPTIONS'),
+      patch: makeSseFn('PATCH'),
+      post: makeSseFn('POST'),
+      put: makeSseFn('PUT'),
+      trace: makeSseFn('TRACE'),
+    },
+    trace: makeMethodFn('TRACE'),
+  } as Client;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/client/index.ts
new file mode 100644
index 0000000000..b295edeca0
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/client/index.ts
@@ -0,0 +1,25 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+export type { Auth } from '../core/auth.gen';
+export type { QuerySerializerOptions } from '../core/bodySerializer.gen';
+export {
+  formDataBodySerializer,
+  jsonBodySerializer,
+  urlSearchParamsBodySerializer,
+} from '../core/bodySerializer.gen';
+export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
+export { createClient } from './client.gen';
+export type {
+  Client,
+  ClientOptions,
+  Config,
+  CreateClientConfig,
+  Options,
+  RequestOptions,
+  RequestResult,
+  ResolvedRequestOptions,
+  ResponseStyle,
+  TDataShape,
+} from './types.gen';
+export { createConfig, mergeHeaders } from './utils.gen';
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/client/types.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/client/types.gen.ts
new file mode 100644
index 0000000000..c80695b84d
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/client/types.gen.ts
@@ -0,0 +1,215 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import type { Auth } from '../core/auth.gen';
+import type {
+  ServerSentEventsOptions,
+  ServerSentEventsResult,
+} from '../core/serverSentEvents.gen';
+import type { Client as CoreClient, Config as CoreConfig } from '../core/types.gen';
+import type { Middleware } from './utils.gen';
+
+export type ResponseStyle = 'data' | 'fields';
+
+export interface Config<T extends ClientOptions = ClientOptions>
+  extends Omit<RequestInit, 'body' | 'headers' | 'method'>, CoreConfig {
+  /**
+   * Base URL for all requests made by this client.
+   */
+  baseUrl?: T['baseUrl'];
+  /**
+   * Fetch API implementation. You can use this option to provide a custom
+   * fetch instance.
+   *
+   * @default globalThis.fetch
+   */
+  fetch?: typeof fetch;
+  /**
+   * Please don't use the Fetch client for Next.js applications. The `next`
+   * options won't have any effect.
+   *
+   * Install {@link https://www.npmjs.com/package/@hey-api/client-next `@hey-api/client-next`} instead.
+   */
+  next?: never;
+  /**
+   * Return the response data parsed in a specified format. By default, `auto`
+   * will infer the appropriate method from the `Content-Type` response header.
+   * You can override this behavior with any of the {@link Body} methods.
+   * Select `stream` if you don't want to parse response data at all.
+   *
+   * @default 'auto'
+   */
+  parseAs?: 'arrayBuffer' | 'auto' | 'blob' | 'formData' | 'json' | 'stream' | 'text';
+  /**
+   * Should we return only data or multiple fields (data, error, response, etc.)?
+   *
+   * @default 'fields'
+   */
+  responseStyle?: ResponseStyle;
+  /**
+   * Throw an error instead of returning it in the response?
+   *
+   * @default false
+   */
+  throwOnError?: T['throwOnError'];
+}
+
+export interface RequestOptions<
+  TData = unknown,
+  TResponseStyle extends ResponseStyle = 'fields',
+  ThrowOnError extends boolean = boolean,
+  Url extends string = string,
+>
+  extends
+    Config<{
+      responseStyle: TResponseStyle;
+      throwOnError: ThrowOnError;
+    }>,
+    Pick<
+      ServerSentEventsOptions<TData>,
+      | 'onRequest'
+      | 'onSseError'
+      | 'onSseEvent'
+      | 'sseDefaultRetryDelay'
+      | 'sseMaxRetryAttempts'
+      | 'sseMaxRetryDelay'
+    > {
+  /**
+   * Any body that you want to add to your request.
+   *
+   * {@link https://developer.mozilla.org/docs/Web/API/fetch#body}
+   */
+  body?: unknown;
+  path?: Record<string, unknown>;
+  query?: Record<string, unknown>;
+  /**
+   * Security mechanism(s) to use for the request.
+   */
+  security?: ReadonlyArray<Auth>;
+  url: Url;
+}
+
+export interface ResolvedRequestOptions<
+  TResponseStyle extends ResponseStyle = 'fields',
+  ThrowOnError extends boolean = boolean,
+  Url extends string = string,
+> extends RequestOptions<unknown, TResponseStyle, ThrowOnError, Url> {
+  headers: Headers;
+  serializedBody?: string;
+}
+
+export type RequestResult<
+  TData = unknown,
+  TError = unknown,
+  ThrowOnError extends boolean = boolean,
+  TResponseStyle extends ResponseStyle = 'fields',
+> = ThrowOnError extends true
+  ? Promise<
+      TResponseStyle extends 'data'
+        ? TData extends Record<string, unknown>
+          ? TData[keyof TData]
+          : TData
+        : {
+            data: TData extends Record<string, unknown> ? TData[keyof TData] : TData;
+            request: Request;
+            response: Response;
+          }
+    >
+  : Promise<
+      TResponseStyle extends 'data'
+        ? (TData extends Record<string, unknown> ? TData[keyof TData] : TData) | undefined
+        : (
+            | {
+                data: TData extends Record<string, unknown> ? TData[keyof TData] : TData;
+                error: undefined;
+              }
+            | {
+                data: undefined;
+                error: TError extends Record<string, unknown> ? TError[keyof TError] : TError;
+              }
+          ) & {
+            request: Request;
+            response: Response;
+          }
+    >;
+
+export interface ClientOptions {
+  baseUrl?: string;
+  responseStyle?: ResponseStyle;
+  throwOnError?: boolean;
+}
+
+type MethodFn = <
+  TData = unknown,
+  TError = unknown,
+  ThrowOnError extends boolean = false,
+  TResponseStyle extends ResponseStyle = 'fields',
+>(
+  options: Omit<RequestOptions<TData, TResponseStyle, ThrowOnError>, 'method'>,
+) => RequestResult<TData, TError, ThrowOnError, TResponseStyle>;
+
+type SseFn = <
+  TData = unknown,
+  TError = unknown,
+  ThrowOnError extends boolean = false,
+  TResponseStyle extends ResponseStyle = 'fields',
+>(
+  options: Omit<RequestOptions<never, TResponseStyle, ThrowOnError>, 'method'>,
+) => Promise<ServerSentEventsResult<TData, TError>>;
+
+type RequestFn = <
+  TData = unknown,
+  TError = unknown,
+  ThrowOnError extends boolean = false,
+  TResponseStyle extends ResponseStyle = 'fields',
+>(
+  options: Omit<RequestOptions<TData, TResponseStyle, ThrowOnError>, 'method'> &
+    Pick<Required<RequestOptions<TData, TResponseStyle, ThrowOnError>>, 'method'>,
+) => RequestResult<TData, TError, ThrowOnError, TResponseStyle>;
+
+type BuildUrlFn = <
+  TData extends {
+    body?: unknown;
+    path?: Record<string, unknown>;
+    query?: Record<string, unknown>;
+    url: string;
+  },
+>(
+  options: TData & Options<TData>,
+) => string;
+
+export type Client = CoreClient<RequestFn, Config, MethodFn, BuildUrlFn, SseFn> & {
+  interceptors: Middleware<Request, Response, unknown, ResolvedRequestOptions>;
+};
+
+/**
+ * The `createClientConfig()` function will be called on client initialization
+ * and the returned object will become the client's initial configuration.
+ *
+ * You may want to initialize your client this way instead of calling
+ * `setConfig()`. This is useful for example if you're using Next.js
+ * to ensure your client always has the correct values.
+ */
+export type CreateClientConfig<T extends ClientOptions = ClientOptions> = (
+  override?: Config<ClientOptions & T>,
+) => Config<Required<ClientOptions> & T>;
+
+export interface TDataShape {
+  body?: unknown;
+  headers?: unknown;
+  path?: unknown;
+  query?: unknown;
+  url: string;
+}
+
+type OmitKeys<T, K> = Pick<T, Exclude<keyof T, K>>;
+
+export type Options<
+  TData extends TDataShape = TDataShape,
+  ThrowOnError extends boolean = boolean,
+  TResponse = unknown,
+  TResponseStyle extends ResponseStyle = 'fields',
+> = OmitKeys<
+  RequestOptions<TResponse, TResponseStyle, ThrowOnError>,
+  'body' | 'path' | 'query' | 'url'
+> &
+  ([TData] extends [never] ? unknown : Omit<TData, 'url'>);
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/client/utils.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/client/utils.gen.ts
new file mode 100644
index 0000000000..5162192d8a
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/client/utils.gen.ts
@@ -0,0 +1,316 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import { getAuthToken } from '../core/auth.gen';
+import type { QuerySerializerOptions } from '../core/bodySerializer.gen';
+import { jsonBodySerializer } from '../core/bodySerializer.gen';
+import {
+  serializeArrayParam,
+  serializeObjectParam,
+  serializePrimitiveParam,
+} from '../core/pathSerializer.gen';
+import { getUrl } from '../core/utils.gen';
+import type { Client, ClientOptions, Config, RequestOptions } from './types.gen';
+
+export const createQuerySerializer = <T = unknown>({
+  parameters = {},
+  ...args
+}: QuerySerializerOptions = {}) => {
+  const querySerializer = (queryParams: T) => {
+    const search: string[] = [];
+    if (queryParams && typeof queryParams === 'object') {
+      for (const name in queryParams) {
+        const value = queryParams[name];
+
+        if (value === undefined || value === null) {
+          continue;
+        }
+
+        const options = parameters[name] || args;
+
+        if (Array.isArray(value)) {
+          const serializedArray = serializeArrayParam({
+            allowReserved: options.allowReserved,
+            explode: true,
+            name,
+            style: 'form',
+            value,
+            ...options.array,
+          });
+          if (serializedArray) search.push(serializedArray);
+        } else if (typeof value === 'object') {
+          const serializedObject = serializeObjectParam({
+            allowReserved: options.allowReserved,
+            explode: true,
+            name,
+            style: 'deepObject',
+            value: value as Record<string, unknown>,
+            ...options.object,
+          });
+          if (serializedObject) search.push(serializedObject);
+        } else {
+          const serializedPrimitive = serializePrimitiveParam({
+            allowReserved: options.allowReserved,
+            name,
+            value: value as string,
+          });
+          if (serializedPrimitive) search.push(serializedPrimitive);
+        }
+      }
+    }
+    return search.join('&');
+  };
+  return querySerializer;
+};
+
+/**
+ * Infers parseAs value from provided Content-Type header.
+ */
+export const getParseAs = (contentType: string | null): Exclude<Config['parseAs'], 'auto'> => {
+  if (!contentType) {
+    // If no Content-Type header is provided, the best we can do is return the raw response body,
+    // which is effectively the same as the 'stream' option.
+    return 'stream';
+  }
+
+  const cleanContent = contentType.split(';')[0]?.trim();
+
+  if (!cleanContent) {
+    return;
+  }
+
+  if (cleanContent.startsWith('application/json') || cleanContent.endsWith('+json')) {
+    return 'json';
+  }
+
+  if (cleanContent === 'multipart/form-data') {
+    return 'formData';
+  }
+
+  if (
+    ['application/', 'audio/', 'image/', 'video/'].some((type) => cleanContent.startsWith(type))
+  ) {
+    return 'blob';
+  }
+
+  if (cleanContent.startsWith('text/')) {
+    return 'text';
+  }
+
+  return;
+};
+
+const checkForExistence = (
+  options: Pick<RequestOptions, 'auth' | 'query'> & {
+    headers: Headers;
+  },
+  name?: string,
+): boolean => {
+  if (!name) {
+    return false;
+  }
+  if (
+    options.headers.has(name) ||
+    options.query?.[name] ||
+    options.headers.get('Cookie')?.includes(`${name}=`)
+  ) {
+    return true;
+  }
+  return false;
+};
+
+export const setAuthParams = async ({
+  security,
+  ...options
+}: Pick<Required<RequestOptions>, 'security'> &
+  Pick<RequestOptions, 'auth' | 'query'> & {
+    headers: Headers;
+  }) => {
+  for (const auth of security) {
+    if (checkForExistence(options, auth.name)) {
+      continue;
+    }
+
+    const token = await getAuthToken(auth, options.auth);
+
+    if (!token) {
+      continue;
+    }
+
+    const name = auth.name ?? 'Authorization';
+
+    switch (auth.in) {
+      case 'query':
+        if (!options.query) {
+          options.query = {};
+        }
+        options.query[name] = token;
+        break;
+      case 'cookie':
+        options.headers.append('Cookie', `${name}=${token}`);
+        break;
+      case 'header':
+      default:
+        options.headers.set(name, token);
+        break;
+    }
+  }
+};
+
+export const buildUrl: Client['buildUrl'] = (options) =>
+  getUrl({
+    baseUrl: options.baseUrl as string,
+    path: options.path,
+    query: options.query,
+    querySerializer:
+      typeof options.querySerializer === 'function'
+        ? options.querySerializer
+        : createQuerySerializer(options.querySerializer),
+    url: options.url,
+  });
+
+export const mergeConfigs = (a: Config, b: Config): Config => {
+  const config = { ...a, ...b };
+  if (config.baseUrl?.endsWith('/')) {
+    config.baseUrl = config.baseUrl.substring(0, config.baseUrl.length - 1);
+  }
+  config.headers = mergeHeaders(a.headers, b.headers);
+  return config;
+};
+
+const headersEntries = (headers: Headers): Array<[string, string]> => {
+  const entries: Array<[string, string]> = [];
+  headers.forEach((value, key) => {
+    entries.push([key, value]);
+  });
+  return entries;
+};
+
+export const mergeHeaders = (
+  ...headers: Array<Required<Config>['headers'] | undefined>
+): Headers => {
+  const mergedHeaders = new Headers();
+  for (const header of headers) {
+    if (!header) {
+      continue;
+    }
+
+    const iterator = header instanceof Headers ? headersEntries(header) : Object.entries(header);
+
+    for (const [key, value] of iterator) {
+      if (value === null) {
+        mergedHeaders.delete(key);
+      } else if (Array.isArray(value)) {
+        for (const v of value) {
+          mergedHeaders.append(key, v as string);
+        }
+      } else if (value !== undefined) {
+        // assume object headers are meant to be JSON stringified, i.e., their
+        // content value in OpenAPI specification is 'application/json'
+        mergedHeaders.set(
+          key,
+          typeof value === 'object' ? JSON.stringify(value) : (value as string),
+        );
+      }
+    }
+  }
+  return mergedHeaders;
+};
+
+type ErrInterceptor<Err, Res, Req, Options> = (
+  error: Err,
+  response: Res,
+  request: Req,
+  options: Options,
+) => Err | Promise<Err>;
+
+type ReqInterceptor<Req, Options> = (request: Req, options: Options) => Req | Promise<Req>;
+
+type ResInterceptor<Res, Req, Options> = (
+  response: Res,
+  request: Req,
+  options: Options,
+) => Res | Promise<Res>;
+
+class Interceptors<Interceptor> {
+  fns: Array<Interceptor | null> = [];
+
+  clear(): void {
+    this.fns = [];
+  }
+
+  eject(id: number | Interceptor): void {
+    const index = this.getInterceptorIndex(id);
+    if (this.fns[index]) {
+      this.fns[index] = null;
+    }
+  }
+
+  exists(id: number | Interceptor): boolean {
+    const index = this.getInterceptorIndex(id);
+    return Boolean(this.fns[index]);
+  }
+
+  getInterceptorIndex(id: number | Interceptor): number {
+    if (typeof id === 'number') {
+      return this.fns[id] ? id : -1;
+    }
+    return this.fns.indexOf(id);
+  }
+
+  update(id: number | Interceptor, fn: Interceptor): number | Interceptor | false {
+    const index = this.getInterceptorIndex(id);
+    if (this.fns[index]) {
+      this.fns[index] = fn;
+      return id;
+    }
+    return false;
+  }
+
+  use(fn: Interceptor): number {
+    this.fns.push(fn);
+    return this.fns.length - 1;
+  }
+}
+
+export interface Middleware<Req, Res, Err, Options> {
+  error: Interceptors<ErrInterceptor<Err, Res, Req, Options>>;
+  request: Interceptors<ReqInterceptor<Req, Options>>;
+  response: Interceptors<ResInterceptor<Res, Req, Options>>;
+}
+
+export const createInterceptors = <Req, Res, Err, Options>(): Middleware<
+  Req,
+  Res,
+  Err,
+  Options
+> => ({
+  error: new Interceptors<ErrInterceptor<Err, Res, Req, Options>>(),
+  request: new Interceptors<ReqInterceptor<Req, Options>>(),
+  response: new Interceptors<ResInterceptor<Res, Req, Options>>(),
+});
+
+const defaultQuerySerializer = createQuerySerializer({
+  allowReserved: false,
+  array: {
+    explode: true,
+    style: 'form',
+  },
+  object: {
+    explode: true,
+    style: 'deepObject',
+  },
+});
+
+const defaultHeaders = {
+  'Content-Type': 'application/json',
+};
+
+export const createConfig = <T extends ClientOptions = ClientOptions>(
+  override: Config<Omit<ClientOptions, keyof T> & T> = {},
+): Config<Omit<ClientOptions, keyof T> & T> => ({
+  ...jsonBodySerializer,
+  headers: defaultHeaders,
+  parseAs: 'auto',
+  querySerializer: defaultQuerySerializer,
+  ...override,
+});
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/auth.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/auth.gen.ts
new file mode 100644
index 0000000000..3ebf994788
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/auth.gen.ts
@@ -0,0 +1,41 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+export type AuthToken = string | undefined;
+
+export interface Auth {
+  /**
+   * Which part of the request do we use to send the auth?
+   *
+   * @default 'header'
+   */
+  in?: 'header' | 'query' | 'cookie';
+  /**
+   * Header or query parameter name.
+   *
+   * @default 'Authorization'
+   */
+  name?: string;
+  scheme?: 'basic' | 'bearer';
+  type: 'apiKey' | 'http';
+}
+
+export const getAuthToken = async (
+  auth: Auth,
+  callback: ((auth: Auth) => Promise<AuthToken> | AuthToken) | AuthToken,
+): Promise<string | undefined> => {
+  const token = typeof callback === 'function' ? await callback(auth) : callback;
+
+  if (!token) {
+    return;
+  }
+
+  if (auth.scheme === 'bearer') {
+    return `Bearer ${token}`;
+  }
+
+  if (auth.scheme === 'basic') {
+    return `Basic ${btoa(token)}`;
+  }
+
+  return token;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/bodySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/bodySerializer.gen.ts
new file mode 100644
index 0000000000..67daca60f8
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/bodySerializer.gen.ts
@@ -0,0 +1,82 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import type { ArrayStyle, ObjectStyle, SerializerOptions } from './pathSerializer.gen';
+
+export type QuerySerializer = (query: Record<string, unknown>) => string;
+
+export type BodySerializer = (body: unknown) => unknown;
+
+type QuerySerializerOptionsObject = {
+  allowReserved?: boolean;
+  array?: Partial<SerializerOptions<ArrayStyle>>;
+  object?: Partial<SerializerOptions<ObjectStyle>>;
+};
+
+export type QuerySerializerOptions = QuerySerializerOptionsObject & {
+  /**
+   * Per-parameter serialization overrides. When provided, these settings
+   * override the global array/object settings for specific parameter names.
+   */
+  parameters?: Record<string, QuerySerializerOptionsObject>;
+};
+
+const serializeFormDataPair = (data: FormData, key: string, value: unknown): void => {
+  if (typeof value === 'string' || value instanceof Blob) {
+    data.append(key, value);
+  } else if (value instanceof Date) {
+    data.append(key, value.toISOString());
+  } else {
+    data.append(key, JSON.stringify(value));
+  }
+};
+
+const serializeUrlSearchParamsPair = (data: URLSearchParams, key: string, value: unknown): void => {
+  if (typeof value === 'string') {
+    data.append(key, value);
+  } else {
+    data.append(key, JSON.stringify(value));
+  }
+};
+
+export const formDataBodySerializer = {
+  bodySerializer: (body: unknown): FormData => {
+    const data = new FormData();
+
+    Object.entries(body as Record<string, unknown>).forEach(([key, value]) => {
+      if (value === undefined || value === null) {
+        return;
+      }
+      if (Array.isArray(value)) {
+        value.forEach((v) => serializeFormDataPair(data, key, v));
+      } else {
+        serializeFormDataPair(data, key, value);
+      }
+    });
+
+    return data;
+  },
+};
+
+export const jsonBodySerializer = {
+  bodySerializer: (body: unknown): string =>
+    JSON.stringify(body, (_key, value) => (typeof value === 'bigint' ? value.toString() : value)),
+};
+
+export const urlSearchParamsBodySerializer = {
+  bodySerializer: (body: unknown): string => {
+    const data = new URLSearchParams();
+
+    Object.entries(body as Record<string, unknown>).forEach(([key, value]) => {
+      if (value === undefined || value === null) {
+        return;
+      }
+      if (Array.isArray(value)) {
+        value.forEach((v) => serializeUrlSearchParamsPair(data, key, v));
+      } else {
+        serializeUrlSearchParamsPair(data, key, value);
+      }
+    });
+
+    return data.toString();
+  },
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/params.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/params.gen.ts
new file mode 100644
index 0000000000..7955601a5c
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/params.gen.ts
@@ -0,0 +1,169 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+type Slot = 'body' | 'headers' | 'path' | 'query';
+
+export type Field =
+  | {
+      in: Exclude<Slot, 'body'>;
+      /**
+       * Field name. This is the name we want the user to see and use.
+       */
+      key: string;
+      /**
+       * Field mapped name. This is the name we want to use in the request.
+       * If omitted, we use the same value as `key`.
+       */
+      map?: string;
+    }
+  | {
+      in: Extract<Slot, 'body'>;
+      /**
+       * Key isn't required for bodies.
+       */
+      key?: string;
+      map?: string;
+    }
+  | {
+      /**
+       * Field name. This is the name we want the user to see and use.
+       */
+      key: string;
+      /**
+       * Field mapped name. This is the name we want to use in the request.
+       * If `in` is omitted, `map` aliases `key` to the transport layer.
+       */
+      map: Slot;
+    };
+
+export interface Fields {
+  allowExtra?: Partial<Record<Slot, boolean>>;
+  args?: ReadonlyArray<Field>;
+}
+
+export type FieldsConfig = ReadonlyArray<Field | Fields>;
+
+const extraPrefixesMap: Record<string, Slot> = {
+  $body_: 'body',
+  $headers_: 'headers',
+  $path_: 'path',
+  $query_: 'query',
+};
+const extraPrefixes = Object.entries(extraPrefixesMap);
+
+type KeyMap = Map<
+  string,
+  | {
+      in: Slot;
+      map?: string;
+    }
+  | {
+      in?: never;
+      map: Slot;
+    }
+>;
+
+const buildKeyMap = (fields: FieldsConfig, map?: KeyMap): KeyMap => {
+  if (!map) {
+    map = new Map();
+  }
+
+  for (const config of fields) {
+    if ('in' in config) {
+      if (config.key) {
+        map.set(config.key, {
+          in: config.in,
+          map: config.map,
+        });
+      }
+    } else if ('key' in config) {
+      map.set(config.key, {
+        map: config.map,
+      });
+    } else if (config.args) {
+      buildKeyMap(config.args, map);
+    }
+  }
+
+  return map;
+};
+
+interface Params {
+  body: unknown;
+  headers: Record<string, unknown>;
+  path: Record<string, unknown>;
+  query: Record<string, unknown>;
+}
+
+const stripEmptySlots = (params: Params) => {
+  for (const [slot, value] of Object.entries(params)) {
+    if (value && typeof value === 'object' && !Array.isArray(value) && !Object.keys(value).length) {
+      delete params[slot as Slot];
+    }
+  }
+};
+
+export const buildClientParams = (args: ReadonlyArray<unknown>, fields: FieldsConfig) => {
+  const params: Params = {
+    body: {},
+    headers: {},
+    path: {},
+    query: {},
+  };
+
+  const map = buildKeyMap(fields);
+
+  let config: FieldsConfig[number] | undefined;
+
+  for (const [index, arg] of args.entries()) {
+    if (fields[index]) {
+      config = fields[index];
+    }
+
+    if (!config) {
+      continue;
+    }
+
+    if ('in' in config) {
+      if (config.key) {
+        const field = map.get(config.key)!;
+        const name = field.map || config.key;
+        if (field.in) {
+          (params[field.in] as Record<string, unknown>)[name] = arg;
+        }
+      } else {
+        params.body = arg;
+      }
+    } else {
+      for (const [key, value] of Object.entries(arg ?? {})) {
+        const field = map.get(key);
+
+        if (field) {
+          if (field.in) {
+            const name = field.map || key;
+            (params[field.in] as Record<string, unknown>)[name] = value;
+          } else {
+            params[field.map] = value;
+          }
+        } else {
+          const extra = extraPrefixes.find(([prefix]) => key.startsWith(prefix));
+
+          if (extra) {
+            const [prefix, slot] = extra;
+            (params[slot] as Record<string, unknown>)[key.slice(prefix.length)] = value;
+          } else if ('allowExtra' in config && config.allowExtra) {
+            for (const [slot, allowed] of Object.entries(config.allowExtra)) {
+              if (allowed) {
+                (params[slot as Slot] as Record<string, unknown>)[key] = value;
+                break;
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+
+  stripEmptySlots(params);
+
+  return params;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/pathSerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/pathSerializer.gen.ts
new file mode 100644
index 0000000000..994b2848c6
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/pathSerializer.gen.ts
@@ -0,0 +1,171 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+interface SerializeOptions<T> extends SerializePrimitiveOptions, SerializerOptions<T> {}
+
+interface SerializePrimitiveOptions {
+  allowReserved?: boolean;
+  name: string;
+}
+
+export interface SerializerOptions<T> {
+  /**
+   * @default true
+   */
+  explode: boolean;
+  style: T;
+}
+
+export type ArrayStyle = 'form' | 'spaceDelimited' | 'pipeDelimited';
+export type ArraySeparatorStyle = ArrayStyle | MatrixStyle;
+type MatrixStyle = 'label' | 'matrix' | 'simple';
+export type ObjectStyle = 'form' | 'deepObject';
+type ObjectSeparatorStyle = ObjectStyle | MatrixStyle;
+
+interface SerializePrimitiveParam extends SerializePrimitiveOptions {
+  value: string;
+}
+
+export const separatorArrayExplode = (style: ArraySeparatorStyle) => {
+  switch (style) {
+    case 'label':
+      return '.';
+    case 'matrix':
+      return ';';
+    case 'simple':
+      return ',';
+    default:
+      return '&';
+  }
+};
+
+export const separatorArrayNoExplode = (style: ArraySeparatorStyle) => {
+  switch (style) {
+    case 'form':
+      return ',';
+    case 'pipeDelimited':
+      return '|';
+    case 'spaceDelimited':
+      return '%20';
+    default:
+      return ',';
+  }
+};
+
+export const separatorObjectExplode = (style: ObjectSeparatorStyle) => {
+  switch (style) {
+    case 'label':
+      return '.';
+    case 'matrix':
+      return ';';
+    case 'simple':
+      return ',';
+    default:
+      return '&';
+  }
+};
+
+export const serializeArrayParam = ({
+  allowReserved,
+  explode,
+  name,
+  style,
+  value,
+}: SerializeOptions<ArraySeparatorStyle> & {
+  value: unknown[];
+}) => {
+  if (!explode) {
+    const joinedValues = (
+      allowReserved ? value : value.map((v) => encodeURIComponent(v as string))
+    ).join(separatorArrayNoExplode(style));
+    switch (style) {
+      case 'label':
+        return `.${joinedValues}`;
+      case 'matrix':
+        return `;${name}=${joinedValues}`;
+      case 'simple':
+        return joinedValues;
+      default:
+        return `${name}=${joinedValues}`;
+    }
+  }
+
+  const separator = separatorArrayExplode(style);
+  const joinedValues = value
+    .map((v) => {
+      if (style === 'label' || style === 'simple') {
+        return allowReserved ? v : encodeURIComponent(v as string);
+      }
+
+      return serializePrimitiveParam({
+        allowReserved,
+        name,
+        value: v as string,
+      });
+    })
+    .join(separator);
+  return style === 'label' || style === 'matrix' ? separator + joinedValues : joinedValues;
+};
+
+export const serializePrimitiveParam = ({
+  allowReserved,
+  name,
+  value,
+}: SerializePrimitiveParam) => {
+  if (value === undefined || value === null) {
+    return '';
+  }
+
+  if (typeof value === 'object') {
+    throw new Error(
+      'Deeply-nested arrays/objects aren’t supported. Provide your own `querySerializer()` to handle these.',
+    );
+  }
+
+  return `${name}=${allowReserved ? value : encodeURIComponent(value)}`;
+};
+
+export const serializeObjectParam = ({
+  allowReserved,
+  explode,
+  name,
+  style,
+  value,
+  valueOnly,
+}: SerializeOptions<ObjectSeparatorStyle> & {
+  value: Record<string, unknown> | Date;
+  valueOnly?: boolean;
+}) => {
+  if (value instanceof Date) {
+    return valueOnly ? value.toISOString() : `${name}=${value.toISOString()}`;
+  }
+
+  if (style !== 'deepObject' && !explode) {
+    let values: string[] = [];
+    Object.entries(value).forEach(([key, v]) => {
+      values = [...values, key, allowReserved ? (v as string) : encodeURIComponent(v as string)];
+    });
+    const joinedValues = values.join(',');
+    switch (style) {
+      case 'form':
+        return `${name}=${joinedValues}`;
+      case 'label':
+        return `.${joinedValues}`;
+      case 'matrix':
+        return `;${name}=${joinedValues}`;
+      default:
+        return joinedValues;
+    }
+  }
+
+  const separator = separatorObjectExplode(style);
+  const joinedValues = Object.entries(value)
+    .map(([key, v]) =>
+      serializePrimitiveParam({
+        allowReserved,
+        name: style === 'deepObject' ? `${name}[${key}]` : key,
+        value: v as string,
+      }),
+    )
+    .join(separator);
+  return style === 'label' || style === 'matrix' ? separator + joinedValues : joinedValues;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..5000df606f
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/queryKeySerializer.gen.ts
@@ -0,0 +1,117 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (value === undefined || typeof value === 'function' || typeof value === 'symbol') {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) => a.localeCompare(b));
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (value: unknown): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (typeof value === 'string' || typeof value === 'number' || typeof value === 'boolean') {
+    return value;
+  }
+
+  if (value === undefined || typeof value === 'function' || typeof value === 'symbol') {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (typeof URLSearchParams !== 'undefined' && value instanceof URLSearchParams) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/serverSentEvents.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/serverSentEvents.gen.ts
new file mode 100644
index 0000000000..ddf3c4d13a
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/serverSentEvents.gen.ts
@@ -0,0 +1,242 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import type { Config } from './types.gen';
+
+export type ServerSentEventsOptions<TData = unknown> = Omit<RequestInit, 'method'> &
+  Pick<Config, 'method' | 'responseTransformer' | 'responseValidator'> & {
+    /**
+     * Fetch API implementation. You can use this option to provide a custom
+     * fetch instance.
+     *
+     * @default globalThis.fetch
+     */
+    fetch?: typeof fetch;
+    /**
+     * Implementing clients can call request interceptors inside this hook.
+     */
+    onRequest?: (url: string, init: RequestInit) => Promise<Request>;
+    /**
+     * Callback invoked when a network or parsing error occurs during streaming.
+     *
+     * This option applies only if the endpoint returns a stream of events.
+     *
+     * @param error The error that occurred.
+     */
+    onSseError?: (error: unknown) => void;
+    /**
+     * Callback invoked when an event is streamed from the server.
+     *
+     * This option applies only if the endpoint returns a stream of events.
+     *
+     * @param event Event streamed from the server.
+     * @returns Nothing (void).
+     */
+    onSseEvent?: (event: StreamEvent<TData>) => void;
+    serializedBody?: RequestInit['body'];
+    /**
+     * Default retry delay in milliseconds.
+     *
+     * This option applies only if the endpoint returns a stream of events.
+     *
+     * @default 3000
+     */
+    sseDefaultRetryDelay?: number;
+    /**
+     * Maximum number of retry attempts before giving up.
+     */
+    sseMaxRetryAttempts?: number;
+    /**
+     * Maximum retry delay in milliseconds.
+     *
+     * Applies only when exponential backoff is used.
+     *
+     * This option applies only if the endpoint returns a stream of events.
+     *
+     * @default 30000
+     */
+    sseMaxRetryDelay?: number;
+    /**
+     * Optional sleep function for retry backoff.
+     *
+     * Defaults to using `setTimeout`.
+     */
+    sseSleepFn?: (ms: number) => Promise<void>;
+    url: string;
+  };
+
+export interface StreamEvent<TData = unknown> {
+  data: TData;
+  event?: string;
+  id?: string;
+  retry?: number;
+}
+
+export type ServerSentEventsResult<TData = unknown, TReturn = void, TNext = unknown> = {
+  stream: AsyncGenerator<
+    TData extends Record<string, unknown> ? TData[keyof TData] : TData,
+    TReturn,
+    TNext
+  >;
+};
+
+export function createSseClient<TData = unknown>({
+  onRequest,
+  onSseError,
+  onSseEvent,
+  responseTransformer,
+  responseValidator,
+  sseDefaultRetryDelay,
+  sseMaxRetryAttempts,
+  sseMaxRetryDelay,
+  sseSleepFn,
+  url,
+  ...options
+}: ServerSentEventsOptions): ServerSentEventsResult<TData> {
+  let lastEventId: string | undefined;
+
+  const sleep = sseSleepFn ?? ((ms: number) => new Promise((resolve) => setTimeout(resolve, ms)));
+
+  const createStream = async function* () {
+    let retryDelay: number = sseDefaultRetryDelay ?? 3000;
+    let attempt = 0;
+    const signal = options.signal ?? new AbortController().signal;
+
+    while (true) {
+      if (signal.aborted) break;
+
+      attempt++;
+
+      const headers =
+        options.headers instanceof Headers
+          ? options.headers
+          : new Headers(options.headers as Record<string, string> | undefined);
+
+      if (lastEventId !== undefined) {
+        headers.set('Last-Event-ID', lastEventId);
+      }
+
+      try {
+        const requestInit: RequestInit = {
+          redirect: 'follow',
+          ...options,
+          body: options.serializedBody,
+          headers,
+          signal,
+        };
+        let request = new Request(url, requestInit);
+        if (onRequest) {
+          request = await onRequest(url, requestInit);
+        }
+        // fetch must be assigned here, otherwise it would throw the error:
+        // TypeError: Failed to execute 'fetch' on 'Window': Illegal invocation
+        const _fetch = options.fetch ?? globalThis.fetch;
+        const response = await _fetch(request);
+
+        if (!response.ok) throw new Error(`SSE failed: ${response.status} ${response.statusText}`);
+
+        if (!response.body) throw new Error('No body in SSE response');
+
+        const reader = response.body.pipeThrough(new TextDecoderStream()).getReader();
+
+        let buffer = '';
+
+        const abortHandler = () => {
+          try {
+            reader.cancel();
+          } catch {
+            // noop
+          }
+        };
+
+        signal.addEventListener('abort', abortHandler);
+
+        try {
+          while (true) {
+            const { done, value } = await reader.read();
+            if (done) break;
+            buffer += value;
+            buffer = buffer.replace(/\r\n?/g, '\n'); // normalize line endings
+
+            const chunks = buffer.split('\n\n');
+            buffer = chunks.pop() ?? '';
+
+            for (const chunk of chunks) {
+              const lines = chunk.split('\n');
+              const dataLines: Array<string> = [];
+              let eventName: string | undefined;
+
+              for (const line of lines) {
+                if (line.startsWith('data:')) {
+                  dataLines.push(line.replace(/^data:\s*/, ''));
+                } else if (line.startsWith('event:')) {
+                  eventName = line.replace(/^event:\s*/, '');
+                } else if (line.startsWith('id:')) {
+                  lastEventId = line.replace(/^id:\s*/, '');
+                } else if (line.startsWith('retry:')) {
+                  const parsed = Number.parseInt(line.replace(/^retry:\s*/, ''), 10);
+                  if (!Number.isNaN(parsed)) {
+                    retryDelay = parsed;
+                  }
+                }
+              }
+
+              let data: unknown;
+              let parsedJson = false;
+
+              if (dataLines.length) {
+                const rawData = dataLines.join('\n');
+                try {
+                  data = JSON.parse(rawData);
+                  parsedJson = true;
+                } catch {
+                  data = rawData;
+                }
+              }
+
+              if (parsedJson) {
+                if (responseValidator) {
+                  await responseValidator(data);
+                }
+
+                if (responseTransformer) {
+                  data = await responseTransformer(data);
+                }
+              }
+
+              onSseEvent?.({
+                data,
+                event: eventName,
+                id: lastEventId,
+                retry: retryDelay,
+              });
+
+              if (dataLines.length) {
+                yield data as any;
+              }
+            }
+          }
+        } finally {
+          signal.removeEventListener('abort', abortHandler);
+          reader.releaseLock();
+        }
+
+        break; // exit loop on normal completion
+      } catch (error) {
+        // connection failed or aborted; retry after delay
+        onSseError?.(error);
+
+        if (sseMaxRetryAttempts !== undefined && attempt >= sseMaxRetryAttempts) {
+          break; // stop after firing error
+        }
+
+        // exponential backoff: double retry each attempt, cap at 30s
+        const backoff = Math.min(retryDelay * 2 ** (attempt - 1), sseMaxRetryDelay ?? 30000);
+        await sleep(backoff);
+      }
+    }
+  };
+
+  const stream = createStream();
+
+  return { stream };
+}
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/types.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/types.gen.ts
new file mode 100644
index 0000000000..9efe71d4c1
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/types.gen.ts
@@ -0,0 +1,104 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import type { Auth, AuthToken } from './auth.gen';
+import type { BodySerializer, QuerySerializer, QuerySerializerOptions } from './bodySerializer.gen';
+
+export type HttpMethod =
+  | 'connect'
+  | 'delete'
+  | 'get'
+  | 'head'
+  | 'options'
+  | 'patch'
+  | 'post'
+  | 'put'
+  | 'trace';
+
+export type Client<
+  RequestFn = never,
+  Config = unknown,
+  MethodFn = never,
+  BuildUrlFn = never,
+  SseFn = never,
+> = {
+  /**
+   * Returns the final request URL.
+   */
+  buildUrl: BuildUrlFn;
+  getConfig: () => Config;
+  request: RequestFn;
+  setConfig: (config: Config) => Config;
+} & {
+  [K in HttpMethod]: MethodFn;
+} & ([SseFn] extends [never] ? { sse?: never } : { sse: { [K in HttpMethod]: SseFn } });
+
+export interface Config {
+  /**
+   * Auth token or a function returning auth token. The resolved value will be
+   * added to the request payload as defined by its `security` array.
+   */
+  auth?: ((auth: Auth) => Promise<AuthToken> | AuthToken) | AuthToken;
+  /**
+   * A function for serializing request body parameter. By default,
+   * {@link JSON.stringify()} will be used.
+   */
+  bodySerializer?: BodySerializer | null;
+  /**
+   * An object containing any HTTP headers that you want to pre-populate your
+   * `Headers` object with.
+   *
+   * {@link https://developer.mozilla.org/docs/Web/API/Headers/Headers#init See more}
+   */
+  headers?:
+    | RequestInit['headers']
+    | Record<
+        string,
+        string | number | boolean | (string | number | boolean)[] | null | undefined | unknown
+      >;
+  /**
+   * The request method.
+   *
+   * {@link https://developer.mozilla.org/docs/Web/API/fetch#method See more}
+   */
+  method?: Uppercase<HttpMethod>;
+  /**
+   * A function for serializing request query parameters. By default, arrays
+   * will be exploded in form style, objects will be exploded in deepObject
+   * style, and reserved characters are percent-encoded.
+   *
+   * This method will have no effect if the native `paramsSerializer()` Axios
+   * API function is used.
+   *
+   * {@link https://swagger.io/docs/specification/serialization/#query View examples}
+   */
+  querySerializer?: QuerySerializer | QuerySerializerOptions;
+  /**
+   * A function validating request data. This is useful if you want to ensure
+   * the request conforms to the desired shape, so it can be safely sent to
+   * the server.
+   */
+  requestValidator?: (data: unknown) => Promise<unknown>;
+  /**
+   * A function transforming response data before it's returned. This is useful
+   * for post-processing data, e.g., converting ISO strings into Date objects.
+   */
+  responseTransformer?: (data: unknown) => Promise<unknown>;
+  /**
+   * A function validating response data. This is useful if you want to ensure
+   * the response conforms to the desired shape, so it can be safely passed to
+   * the transformers and returned to the user.
+   */
+  responseValidator?: (data: unknown) => Promise<unknown>;
+}
+
+type IsExactlyNeverOrNeverUndefined<T> = [T] extends [never]
+  ? true
+  : [T] extends [never | undefined]
+    ? [undefined] extends [T]
+      ? false
+      : true
+    : false;
+
+export type OmitNever<T extends Record<string, unknown>> = {
+  [K in keyof T as IsExactlyNeverOrNeverUndefined<T[K]> extends true ? never : K]: T[K];
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/utils.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/utils.gen.ts
new file mode 100644
index 0000000000..9a4fec7830
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/core/utils.gen.ts
@@ -0,0 +1,140 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import type { BodySerializer, QuerySerializer } from './bodySerializer.gen';
+import {
+  type ArraySeparatorStyle,
+  serializeArrayParam,
+  serializeObjectParam,
+  serializePrimitiveParam,
+} from './pathSerializer.gen';
+
+export interface PathSerializer {
+  path: Record<string, unknown>;
+  url: string;
+}
+
+export const PATH_PARAM_RE = /\{[^{}]+\}/g;
+
+export const defaultPathSerializer = ({ path, url: _url }: PathSerializer) => {
+  let url = _url;
+  const matches = _url.match(PATH_PARAM_RE);
+  if (matches) {
+    for (const match of matches) {
+      let explode = false;
+      let name = match.substring(1, match.length - 1);
+      let style: ArraySeparatorStyle = 'simple';
+
+      if (name.endsWith('*')) {
+        explode = true;
+        name = name.substring(0, name.length - 1);
+      }
+
+      if (name.startsWith('.')) {
+        name = name.substring(1);
+        style = 'label';
+      } else if (name.startsWith(';')) {
+        name = name.substring(1);
+        style = 'matrix';
+      }
+
+      const value = path[name];
+
+      if (value === undefined || value === null) {
+        continue;
+      }
+
+      if (Array.isArray(value)) {
+        url = url.replace(match, serializeArrayParam({ explode, name, style, value }));
+        continue;
+      }
+
+      if (typeof value === 'object') {
+        url = url.replace(
+          match,
+          serializeObjectParam({
+            explode,
+            name,
+            style,
+            value: value as Record<string, unknown>,
+            valueOnly: true,
+          }),
+        );
+        continue;
+      }
+
+      if (style === 'matrix') {
+        url = url.replace(
+          match,
+          `;${serializePrimitiveParam({
+            name,
+            value: value as string,
+          })}`,
+        );
+        continue;
+      }
+
+      const replaceValue = encodeURIComponent(
+        style === 'label' ? `.${value as string}` : (value as string),
+      );
+      url = url.replace(match, replaceValue);
+    }
+  }
+  return url;
+};
+
+export const getUrl = ({
+  baseUrl,
+  path,
+  query,
+  querySerializer,
+  url: _url,
+}: {
+  baseUrl?: string;
+  path?: Record<string, unknown>;
+  query?: Record<string, unknown>;
+  querySerializer: QuerySerializer;
+  url: string;
+}) => {
+  const pathUrl = _url.startsWith('/') ? _url : `/${_url}`;
+  let url = (baseUrl ?? '') + pathUrl;
+  if (path) {
+    url = defaultPathSerializer({ path, url });
+  }
+  let search = query ? querySerializer(query) : '';
+  if (search.startsWith('?')) {
+    search = search.substring(1);
+  }
+  if (search) {
+    url += `?${search}`;
+  }
+  return url;
+};
+
+export function getValidRequestBody(options: {
+  body?: unknown;
+  bodySerializer?: BodySerializer | null;
+  serializedBody?: unknown;
+}) {
+  const hasBody = options.body !== undefined;
+  const isSerializedBody = hasBody && options.bodySerializer;
+
+  if (isSerializedBody) {
+    if ('serializedBody' in options) {
+      const hasSerializedBody =
+        options.serializedBody !== undefined && options.serializedBody !== '';
+
+      return hasSerializedBody ? options.serializedBody : null;
+    }
+
+    // not all clients implement a serializedBody property (i.e., client-axios)
+    return options.body !== '' ? options.body : null;
+  }
+
+  // plain/text body
+  if (hasBody) {
+    return options.body;
+  }
+
+  // no body was provided
+  return undefined;
+}
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/index.ts
new file mode 100644
index 0000000000..eae5951f81
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/index.ts
@@ -0,0 +1,4 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+export { type Options, RequestOperations_describeHTTPRequest } from './sdk.gen';
+export type { ClientOptions, HTTPError, HTTPRequest, RequestOperations_describeHTTPRequestData, RequestOperations_describeHTTPRequestError, RequestOperations_describeHTTPRequestErrors, RequestOperations_describeHTTPRequestResponse, RequestOperations_describeHTTPRequestResponses } from './types.gen';
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/sdk.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/sdk.gen.ts
new file mode 100644
index 0000000000..4359e74459
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/sdk.gen.ts
@@ -0,0 +1,21 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import type { Client, Options as Options2, TDataShape } from './client';
+import { client } from './client.gen';
+import type { RequestOperations_describeHTTPRequestData, RequestOperations_describeHTTPRequestErrors, RequestOperations_describeHTTPRequestResponses } from './types.gen';
+
+export type Options<TData extends TDataShape = TDataShape, ThrowOnError extends boolean = boolean, TResponse = unknown> = Options2<TData, ThrowOnError, TResponse> & {
+    /**
+     * You can provide a client instance returned by `createClient()` instead of
+     * individual options. This might be also useful if you want to implement a
+     * custom client.
+     */
+    client?: Client;
+    /**
+     * You can pass arbitrary values through the `meta` object. This can be
+     * used to access values that aren't defined as part of the SDK function.
+     */
+    meta?: Record<string, unknown>;
+};
+
+export const RequestOperations_describeHTTPRequest = <ThrowOnError extends boolean = false>(options: Options<RequestOperations_describeHTTPRequestData, ThrowOnError>) => (options.client ?? client).get<RequestOperations_describeHTTPRequestResponses, RequestOperations_describeHTTPRequestErrors, ThrowOnError>({ url: '/requests/{id}', ...options });
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/types.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/types.gen.ts
new file mode 100644
index 0000000000..1ba00c7e43
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve-sdk/types.gen.ts
@@ -0,0 +1,40 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+export type ClientOptions = {
+    baseUrl: `${string}://${string}` | (string & {});
+};
+
+export type HTTPRequest = {
+    id: string;
+};
+
+export type HTTPError = {
+    message: string;
+};
+
+export type RequestOperations_describeHTTPRequestData = {
+    body?: never;
+    path: {
+        id: string;
+    };
+    query?: never;
+    url: '/requests/{id}';
+};
+
+export type RequestOperations_describeHTTPRequestErrors = {
+    /**
+     * Not Found
+     */
+    404: HTTPError;
+};
+
+export type RequestOperations_describeHTTPRequestError = RequestOperations_describeHTTPRequestErrors[keyof RequestOperations_describeHTTPRequestErrors];
+
+export type RequestOperations_describeHTTPRequestResponses = {
+    /**
+     * OK
+     */
+    200: HTTPRequest;
+};
+
+export type RequestOperations_describeHTTPRequestResponse = RequestOperations_describeHTTPRequestResponses[keyof RequestOperations_describeHTTPRequestResponses];
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve/index.ts
new file mode 100644
index 0000000000..ceb7a78536
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve/index.ts
@@ -0,0 +1,3 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+export type { ClientOptions, HTTPError, HTTPRequest, RequestOperations_describeHTTPRequestData, RequestOperations_describeHTTPRequestError, RequestOperations_describeHTTPRequestErrors, RequestOperations_describeHTTPRequestResponse, RequestOperations_describeHTTPRequestResponses } from './types.gen';
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve/types.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve/types.gen.ts
new file mode 100644
index 0000000000..1ba00c7e43
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/acronym-operationid-preserve/types.gen.ts
@@ -0,0 +1,40 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+export type ClientOptions = {
+    baseUrl: `${string}://${string}` | (string & {});
+};
+
+export type HTTPRequest = {
+    id: string;
+};
+
+export type HTTPError = {
+    message: string;
+};
+
+export type RequestOperations_describeHTTPRequestData = {
+    body?: never;
+    path: {
+        id: string;
+    };
+    query?: never;
+    url: '/requests/{id}';
+};
+
+export type RequestOperations_describeHTTPRequestErrors = {
+    /**
+     * Not Found
+     */
+    404: HTTPError;
+};
+
+export type RequestOperations_describeHTTPRequestError = RequestOperations_describeHTTPRequestErrors[keyof RequestOperations_describeHTTPRequestErrors];
+
+export type RequestOperations_describeHTTPRequestResponses = {
+    /**
+     * OK
+     */
+    200: HTTPRequest;
+};
+
+export type RequestOperations_describeHTTPRequestResponse = RequestOperations_describeHTTPRequestResponses[keyof RequestOperations_describeHTTPRequestResponses];
diff --git a/packages/openapi-ts-tests/valibot/v1/__snapshots__/3.1.x/acronym-operationid-preserve/valibot.gen.ts b/packages/openapi-ts-tests/valibot/v1/__snapshots__/3.1.x/acronym-operationid-preserve/valibot.gen.ts
new file mode 100644
index 0000000000..9e09f9442d
--- /dev/null
+++ b/packages/openapi-ts-tests/valibot/v1/__snapshots__/3.1.x/acronym-operationid-preserve/valibot.gen.ts
@@ -0,0 +1,20 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import * as v from 'valibot';
+
+export const vHTTPRequest = v.object({
+    id: v.string()
+});
+
+export const vHTTPError = v.object({
+    message: v.string()
+});
+
+export const vRequestOperations_describeHTTPRequestPath = v.object({
+    id: v.string()
+});
+
+/**
+ * OK
+ */
+export const vRequestOperations_describeHTTPRequestResponse = vHTTPRequest;
diff --git a/packages/openapi-ts-tests/valibot/v1/test/3.1.x.test.ts b/packages/openapi-ts-tests/valibot/v1/test/3.1.x.test.ts
index 13e5671aef..8222cd4130 100644
--- a/packages/openapi-ts-tests/valibot/v1/test/3.1.x.test.ts
+++ b/packages/openapi-ts-tests/valibot/v1/test/3.1.x.test.ts
@@ -175,6 +175,19 @@ describe(`OpenAPI ${version}`, () => {
       }),
       description: 'handles various schema types and formats',
     },
+    {
+      config: createConfig({
+        input: 'acronym-operationid-preserve.yaml',
+        output: 'acronym-operationid-preserve',
+        plugins: [
+          {
+            case: 'preserve',
+            name: 'valibot',
+          },
+        ],
+      }),
+      description: 'preserves acronym casing from operationId when case is preserve',
+    },
   ];
 
   it.each(scenarios)('$description', async ({ config }) => {
diff --git a/packages/openapi-ts-tests/zod/v3/__snapshots__/3.1.x/mini/acronym-operationid-preserve/zod.gen.ts b/packages/openapi-ts-tests/zod/v3/__snapshots__/3.1.x/mini/acronym-operationid-preserve/zod.gen.ts
new file mode 100644
index 0000000000..bd7ecf3749
--- /dev/null
+++ b/packages/openapi-ts-tests/zod/v3/__snapshots__/3.1.x/mini/acronym-operationid-preserve/zod.gen.ts
@@ -0,0 +1,20 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import { z } from 'zod';
+
+export const zHTTPRequest = z.object({
+    id: z.string()
+});
+
+export const zHTTPError = z.object({
+    message: z.string()
+});
+
+export const zRequestOperations_describeHTTPRequestPath = z.object({
+    id: z.string()
+});
+
+/**
+ * OK
+ */
+export const zRequestOperations_describeHTTPRequestResponse = zHTTPRequest;
diff --git a/packages/openapi-ts-tests/zod/v3/__snapshots__/3.1.x/v3/acronym-operationid-preserve/zod.gen.ts b/packages/openapi-ts-tests/zod/v3/__snapshots__/3.1.x/v3/acronym-operationid-preserve/zod.gen.ts
new file mode 100644
index 0000000000..bd7ecf3749
--- /dev/null
+++ b/packages/openapi-ts-tests/zod/v3/__snapshots__/3.1.x/v3/acronym-operationid-preserve/zod.gen.ts
@@ -0,0 +1,20 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import { z } from 'zod';
+
+export const zHTTPRequest = z.object({
+    id: z.string()
+});
+
+export const zHTTPError = z.object({
+    message: z.string()
+});
+
+export const zRequestOperations_describeHTTPRequestPath = z.object({
+    id: z.string()
+});
+
+/**
+ * OK
+ */
+export const zRequestOperations_describeHTTPRequestResponse = zHTTPRequest;
diff --git a/packages/openapi-ts-tests/zod/v3/__snapshots__/3.1.x/v4/acronym-operationid-preserve/zod.gen.ts b/packages/openapi-ts-tests/zod/v3/__snapshots__/3.1.x/v4/acronym-operationid-preserve/zod.gen.ts
new file mode 100644
index 0000000000..bd7ecf3749
--- /dev/null
+++ b/packages/openapi-ts-tests/zod/v3/__snapshots__/3.1.x/v4/acronym-operationid-preserve/zod.gen.ts
@@ -0,0 +1,20 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import { z } from 'zod';
+
+export const zHTTPRequest = z.object({
+    id: z.string()
+});
+
+export const zHTTPError = z.object({
+    message: z.string()
+});
+
+export const zRequestOperations_describeHTTPRequestPath = z.object({
+    id: z.string()
+});
+
+/**
+ * OK
+ */
+export const zRequestOperations_describeHTTPRequestResponse = zHTTPRequest;
diff --git a/packages/openapi-ts-tests/zod/v3/test/3.1.x.test.ts b/packages/openapi-ts-tests/zod/v3/test/3.1.x.test.ts
index 5761d3ba64..05ab58ce9f 100644
--- a/packages/openapi-ts-tests/zod/v3/test/3.1.x.test.ts
+++ b/packages/openapi-ts-tests/zod/v3/test/3.1.x.test.ts
@@ -183,6 +183,19 @@ for (const zodVersion of zodVersions) {
         }),
         description: 'generates permissive enums with enum resolver',
       },
+      {
+        config: createConfig({
+          input: 'acronym-operationid-preserve.yaml',
+          output: 'acronym-operationid-preserve',
+          plugins: [
+            {
+              case: 'preserve',
+              name: 'zod',
+            },
+          ],
+        }),
+        description: 'preserves acronym casing from operationId when case is preserve',
+      },
     ];
 
     it.each(scenarios)('$description', async ({ config }) => {
diff --git a/packages/openapi-ts-tests/zod/v4/__snapshots__/3.1.x/mini/acronym-operationid-preserve/zod.gen.ts b/packages/openapi-ts-tests/zod/v4/__snapshots__/3.1.x/mini/acronym-operationid-preserve/zod.gen.ts
new file mode 100644
index 0000000000..2339290e49
--- /dev/null
+++ b/packages/openapi-ts-tests/zod/v4/__snapshots__/3.1.x/mini/acronym-operationid-preserve/zod.gen.ts
@@ -0,0 +1,20 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import * as z from 'zod';
+
+export const zHTTPRequest = z.object({
+    id: z.string()
+});
+
+export const zHTTPError = z.object({
+    message: z.string()
+});
+
+export const zRequestOperations_describeHTTPRequestPath = z.object({
+    id: z.string()
+});
+
+/**
+ * OK
+ */
+export const zRequestOperations_describeHTTPRequestResponse = zHTTPRequest;
diff --git a/packages/openapi-ts-tests/zod/v4/__snapshots__/3.1.x/v3/acronym-operationid-preserve/zod.gen.ts b/packages/openapi-ts-tests/zod/v4/__snapshots__/3.1.x/v3/acronym-operationid-preserve/zod.gen.ts
new file mode 100644
index 0000000000..2339290e49
--- /dev/null
+++ b/packages/openapi-ts-tests/zod/v4/__snapshots__/3.1.x/v3/acronym-operationid-preserve/zod.gen.ts
@@ -0,0 +1,20 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import * as z from 'zod';
+
+export const zHTTPRequest = z.object({
+    id: z.string()
+});
+
+export const zHTTPError = z.object({
+    message: z.string()
+});
+
+export const zRequestOperations_describeHTTPRequestPath = z.object({
+    id: z.string()
+});
+
+/**
+ * OK
+ */
+export const zRequestOperations_describeHTTPRequestResponse = zHTTPRequest;
diff --git a/packages/openapi-ts-tests/zod/v4/__snapshots__/3.1.x/v4/acronym-operationid-preserve/zod.gen.ts b/packages/openapi-ts-tests/zod/v4/__snapshots__/3.1.x/v4/acronym-operationid-preserve/zod.gen.ts
new file mode 100644
index 0000000000..2339290e49
--- /dev/null
+++ b/packages/openapi-ts-tests/zod/v4/__snapshots__/3.1.x/v4/acronym-operationid-preserve/zod.gen.ts
@@ -0,0 +1,20 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import * as z from 'zod';
+
+export const zHTTPRequest = z.object({
+    id: z.string()
+});
+
+export const zHTTPError = z.object({
+    message: z.string()
+});
+
+export const zRequestOperations_describeHTTPRequestPath = z.object({
+    id: z.string()
+});
+
+/**
+ * OK
+ */
+export const zRequestOperations_describeHTTPRequestResponse = zHTTPRequest;
diff --git a/packages/openapi-ts-tests/zod/v4/test/3.1.x.test.ts b/packages/openapi-ts-tests/zod/v4/test/3.1.x.test.ts
index 205cf4d10f..6949e7a2ae 100644
--- a/packages/openapi-ts-tests/zod/v4/test/3.1.x.test.ts
+++ b/packages/openapi-ts-tests/zod/v4/test/3.1.x.test.ts
@@ -208,6 +208,19 @@ for (const zodVersion of zodVersions) {
         }),
         description: 'generates permissive enums with enum resolver',
       },
+      {
+        config: createConfig({
+          input: 'acronym-operationid-preserve.yaml',
+          output: 'acronym-operationid-preserve',
+          plugins: [
+            {
+              case: 'preserve',
+              name: 'zod',
+            },
+          ],
+        }),
+        description: 'preserves acronym casing from operationId when case is preserve',
+      },
     ];
 
     it.each(scenarios)('$description', async ({ config }) => {
diff --git a/packages/openapi-ts/src/plugins/@hey-api/typescript/shared/operation.ts b/packages/openapi-ts/src/plugins/@hey-api/typescript/shared/operation.ts
index afef704b0d..a83c1c5aab 100644
--- a/packages/openapi-ts/src/plugins/@hey-api/typescript/shared/operation.ts
+++ b/packages/openapi-ts/src/plugins/@hey-api/typescript/shared/operation.ts
@@ -1,5 +1,10 @@
 import type { IR } from '@hey-api/shared';
-import { buildSymbolIn, deduplicateSchema, operationResponsesMap } from '@hey-api/shared';
+import {
+  buildSymbolIn,
+  deduplicateSchema,
+  operationBaseName,
+  operationResponsesMap,
+} from '@hey-api/shared';
 
 import { $ } from '../../../../ts-dsl';
 import type { HeyApiTypeScriptPlugin } from '../types';
@@ -126,7 +131,7 @@ export const operationToType = ({
         tags,
         tool: 'typescript',
       },
-      name: operation.id,
+      name: operationBaseName(operation),
       naming: plugin.config.requests,
       operation,
       plugin,
@@ -164,7 +169,7 @@ export const operationToType = ({
           tags,
           tool: 'typescript',
         },
-        name: operation.id,
+        name: operationBaseName(operation),
         naming: plugin.config.errors,
         operation,
         plugin,
@@ -188,7 +193,7 @@ export const operationToType = ({
             tags,
             tool: 'typescript',
           },
-          name: operation.id,
+          name: operationBaseName(operation),
           naming: {
             case: plugin.config.errors.case,
             name: plugin.config.errors.error,
@@ -229,7 +234,7 @@ export const operationToType = ({
           tags,
           tool: 'typescript',
         },
-        name: operation.id,
+        name: operationBaseName(operation),
         naming: plugin.config.responses,
         operation,
         plugin,
@@ -253,7 +258,7 @@ export const operationToType = ({
             tags,
             tool: 'typescript',
           },
-          name: operation.id,
+          name: operationBaseName(operation),
           naming: {
             case: plugin.config.responses.case,
             name: plugin.config.responses.response,
diff --git a/packages/openapi-ts/src/plugins/@hey-api/typescript/shared/webhook.ts b/packages/openapi-ts/src/plugins/@hey-api/typescript/shared/webhook.ts
index 1bd5ed5f1c..603899ec6c 100644
--- a/packages/openapi-ts/src/plugins/@hey-api/typescript/shared/webhook.ts
+++ b/packages/openapi-ts/src/plugins/@hey-api/typescript/shared/webhook.ts
@@ -1,6 +1,6 @@
 import type { Symbol } from '@hey-api/codegen-core';
 import type { IR } from '@hey-api/shared';
-import { buildSymbolIn } from '@hey-api/shared';
+import { buildSymbolIn, operationBaseName } from '@hey-api/shared';
 
 import { createSchemaComment } from '../../../../plugins/shared/utils/schema';
 import { $ } from '../../../../ts-dsl';
@@ -33,7 +33,7 @@ export function webhookToType({
           tags,
           tool: 'typescript',
         },
-        name: operation.id,
+        name: operationBaseName(operation),
         naming: {
           case: plugin.config.webhooks.case,
           name: plugin.config.webhooks.payload,
@@ -85,7 +85,7 @@ export function webhookToType({
         tags,
         tool: 'typescript',
       },
-      name: operation.id,
+      name: operationBaseName(operation),
       naming: plugin.config.webhooks,
       operation,
       plugin,
diff --git a/packages/openapi-ts/src/plugins/valibot/shared/operation.ts b/packages/openapi-ts/src/plugins/valibot/shared/operation.ts
index 8462e3d382..74f01b70b9 100644
--- a/packages/openapi-ts/src/plugins/valibot/shared/operation.ts
+++ b/packages/openapi-ts/src/plugins/valibot/shared/operation.ts
@@ -1,5 +1,5 @@
 import type { IR } from '@hey-api/shared';
-import { operationResponsesMap } from '@hey-api/shared';
+import { operationBaseName, operationResponsesMap } from '@hey-api/shared';
 
 import { buildOperationSchema } from './operation-schema';
 import type { ProcessorContext, ProcessorResult } from './processor';
@@ -25,7 +25,7 @@ export function irOperationToAst({
           role: 'request-body',
         },
         naming: plugin.config.requests.body,
-        namingAnchor: operation.id,
+        namingAnchor: operationBaseName(operation),
         path: [...path, 'body'],
         plugin,
         schema: schema.properties.body,
@@ -43,7 +43,7 @@ export function irOperationToAst({
           role: 'request-headers',
         },
         naming: plugin.config.requests.headers,
-        namingAnchor: operation.id,
+        namingAnchor: operationBaseName(operation),
         path: [...path, 'headers'],
         plugin,
         schema: schema.properties.headers,
@@ -59,7 +59,7 @@ export function irOperationToAst({
           role: 'request-path',
         },
         naming: plugin.config.requests.path,
-        namingAnchor: operation.id,
+        namingAnchor: operationBaseName(operation),
         path: [...path, 'path'],
         plugin,
         schema: schema.properties.path,
@@ -75,7 +75,7 @@ export function irOperationToAst({
           role: 'request-query',
         },
         naming: plugin.config.requests.query,
-        namingAnchor: operation.id,
+        namingAnchor: operationBaseName(operation),
         path: [...path, 'query'],
         plugin,
         schema: schema.properties.query,
@@ -96,7 +96,7 @@ export function irOperationToAst({
             role: 'responses',
           },
           naming: plugin.config.responses,
-          namingAnchor: operation.id,
+          namingAnchor: operationBaseName(operation),
           path: [...path, 'responses'],
           plugin,
           schema: response,
diff --git a/packages/openapi-ts/src/plugins/valibot/shared/webhook.ts b/packages/openapi-ts/src/plugins/valibot/shared/webhook.ts
index 341d46549a..13eaa211ae 100644
--- a/packages/openapi-ts/src/plugins/valibot/shared/webhook.ts
+++ b/packages/openapi-ts/src/plugins/valibot/shared/webhook.ts
@@ -1,4 +1,5 @@
 import type { IR } from '@hey-api/shared';
+import { operationBaseName } from '@hey-api/shared';
 
 import { buildOperationSchema } from './operation-schema';
 import type { ProcessorContext, ProcessorResult } from './processor';
@@ -23,7 +24,7 @@ export function irWebhookToAst({
         role: 'data',
       },
       naming: plugin.config.webhooks,
-      namingAnchor: operation.id,
+      namingAnchor: operationBaseName(operation),
       path,
       plugin,
       schema,
diff --git a/packages/openapi-ts/src/plugins/valibot/v1/api.ts b/packages/openapi-ts/src/plugins/valibot/v1/api.ts
index a8f6baf31a..98f7fdf249 100644
--- a/packages/openapi-ts/src/plugins/valibot/v1/api.ts
+++ b/packages/openapi-ts/src/plugins/valibot/v1/api.ts
@@ -1,6 +1,6 @@
 import type { Symbol } from '@hey-api/codegen-core';
 import type { RequestSchemaContext, ResolvedRequestValidatorLayer } from '@hey-api/shared';
-import { requestValidatorLayers, resolveValidatorLayer } from '@hey-api/shared';
+import { operationBaseName, requestValidatorLayers, resolveValidatorLayer } from '@hey-api/shared';
 
 import { $ } from '../../../ts-dsl';
 import type {
@@ -177,7 +177,7 @@ export function createRequestSchemaV1(
       role: 'data',
     },
     naming: plugin.config.requests,
-    namingAnchor: operation.id,
+    namingAnchor: operationBaseName(operation),
     path: [],
     plugin,
     schema: {},
diff --git a/packages/openapi-ts/src/plugins/zod/mini/api.ts b/packages/openapi-ts/src/plugins/zod/mini/api.ts
index 9ff5e7e37f..c55994b46f 100644
--- a/packages/openapi-ts/src/plugins/zod/mini/api.ts
+++ b/packages/openapi-ts/src/plugins/zod/mini/api.ts
@@ -1,6 +1,6 @@
 import type { Symbol } from '@hey-api/codegen-core';
 import type { RequestSchemaContext, ResolvedRequestValidatorLayer } from '@hey-api/shared';
-import { requestValidatorLayers, resolveValidatorLayer } from '@hey-api/shared';
+import { operationBaseName, requestValidatorLayers, resolveValidatorLayer } from '@hey-api/shared';
 
 import { $ } from '../../../ts-dsl';
 import { identifiers } from '../constants';
@@ -175,7 +175,7 @@ export function createRequestSchemaMini(
       role: 'data',
     },
     naming: plugin.config.requests,
-    namingAnchor: operation.id,
+    namingAnchor: operationBaseName(operation),
     path: [],
     plugin,
     schema: {},
diff --git a/packages/openapi-ts/src/plugins/zod/shared/operation.ts b/packages/openapi-ts/src/plugins/zod/shared/operation.ts
index 8462e3d382..74f01b70b9 100644
--- a/packages/openapi-ts/src/plugins/zod/shared/operation.ts
+++ b/packages/openapi-ts/src/plugins/zod/shared/operation.ts
@@ -1,5 +1,5 @@
 import type { IR } from '@hey-api/shared';
-import { operationResponsesMap } from '@hey-api/shared';
+import { operationBaseName, operationResponsesMap } from '@hey-api/shared';
 
 import { buildOperationSchema } from './operation-schema';
 import type { ProcessorContext, ProcessorResult } from './processor';
@@ -25,7 +25,7 @@ export function irOperationToAst({
           role: 'request-body',
         },
         naming: plugin.config.requests.body,
-        namingAnchor: operation.id,
+        namingAnchor: operationBaseName(operation),
         path: [...path, 'body'],
         plugin,
         schema: schema.properties.body,
@@ -43,7 +43,7 @@ export function irOperationToAst({
           role: 'request-headers',
         },
         naming: plugin.config.requests.headers,
-        namingAnchor: operation.id,
+        namingAnchor: operationBaseName(operation),
         path: [...path, 'headers'],
         plugin,
         schema: schema.properties.headers,
@@ -59,7 +59,7 @@ export function irOperationToAst({
           role: 'request-path',
         },
         naming: plugin.config.requests.path,
-        namingAnchor: operation.id,
+        namingAnchor: operationBaseName(operation),
         path: [...path, 'path'],
         plugin,
         schema: schema.properties.path,
@@ -75,7 +75,7 @@ export function irOperationToAst({
           role: 'request-query',
         },
         naming: plugin.config.requests.query,
-        namingAnchor: operation.id,
+        namingAnchor: operationBaseName(operation),
         path: [...path, 'query'],
         plugin,
         schema: schema.properties.query,
@@ -96,7 +96,7 @@ export function irOperationToAst({
             role: 'responses',
           },
           naming: plugin.config.responses,
-          namingAnchor: operation.id,
+          namingAnchor: operationBaseName(operation),
           path: [...path, 'responses'],
           plugin,
           schema: response,
diff --git a/packages/openapi-ts/src/plugins/zod/shared/webhook.ts b/packages/openapi-ts/src/plugins/zod/shared/webhook.ts
index 341d46549a..13eaa211ae 100644
--- a/packages/openapi-ts/src/plugins/zod/shared/webhook.ts
+++ b/packages/openapi-ts/src/plugins/zod/shared/webhook.ts
@@ -1,4 +1,5 @@
 import type { IR } from '@hey-api/shared';
+import { operationBaseName } from '@hey-api/shared';
 
 import { buildOperationSchema } from './operation-schema';
 import type { ProcessorContext, ProcessorResult } from './processor';
@@ -23,7 +24,7 @@ export function irWebhookToAst({
         role: 'data',
       },
       naming: plugin.config.webhooks,
-      namingAnchor: operation.id,
+      namingAnchor: operationBaseName(operation),
       path,
       plugin,
       schema,
diff --git a/packages/openapi-ts/src/plugins/zod/v3/api.ts b/packages/openapi-ts/src/plugins/zod/v3/api.ts
index 7200e48164..58bc9f65a3 100644
--- a/packages/openapi-ts/src/plugins/zod/v3/api.ts
+++ b/packages/openapi-ts/src/plugins/zod/v3/api.ts
@@ -1,6 +1,6 @@
 import type { Symbol } from '@hey-api/codegen-core';
 import type { RequestSchemaContext, ResolvedRequestValidatorLayer } from '@hey-api/shared';
-import { requestValidatorLayers, resolveValidatorLayer } from '@hey-api/shared';
+import { operationBaseName, requestValidatorLayers, resolveValidatorLayer } from '@hey-api/shared';
 
 import { $ } from '../../../ts-dsl';
 import { identifiers } from '../constants';
@@ -174,7 +174,7 @@ export function createRequestSchemaV3(
       role: 'data',
     },
     naming: plugin.config.requests,
-    namingAnchor: operation.id,
+    namingAnchor: operationBaseName(operation),
     path: [],
     plugin,
     schema: {},
diff --git a/packages/openapi-ts/src/plugins/zod/v4/api.ts b/packages/openapi-ts/src/plugins/zod/v4/api.ts
index 7e3c84149e..5a5c704aa4 100644
--- a/packages/openapi-ts/src/plugins/zod/v4/api.ts
+++ b/packages/openapi-ts/src/plugins/zod/v4/api.ts
@@ -1,6 +1,6 @@
 import type { Symbol } from '@hey-api/codegen-core';
 import type { RequestSchemaContext, ResolvedRequestValidatorLayer } from '@hey-api/shared';
-import { requestValidatorLayers, resolveValidatorLayer } from '@hey-api/shared';
+import { operationBaseName, requestValidatorLayers, resolveValidatorLayer } from '@hey-api/shared';
 
 import { $ } from '../../../ts-dsl';
 import { identifiers } from '../constants';
@@ -174,7 +174,7 @@ export function createRequestSchemaV4(
       role: 'data',
     },
     naming: plugin.config.requests,
-    namingAnchor: operation.id,
+    namingAnchor: operationBaseName(operation),
     path: [],
     plugin,
     schema: {},
diff --git a/packages/shared/src/index.ts b/packages/shared/src/index.ts
index dc6eecc088..c121255832 100644
--- a/packages/shared/src/index.ts
+++ b/packages/shared/src/index.ts
@@ -88,6 +88,7 @@ export type { OperationsStrategy } from './openApi/shared/locations';
 export type { OperationPathStrategy, OperationStructureStrategy } from './openApi/shared/locations';
 export { OperationPath, OperationStrategy } from './openApi/shared/locations';
 export { buildGraph } from './openApi/shared/utils/graph';
+export { operationBaseName } from './openApi/shared/utils/operation';
 export { patchOpenApiSpec } from './openApi/shared/utils/patch';
 export type {
   OpenApi,
diff --git a/packages/shared/src/openApi/shared/locations/operation.ts b/packages/shared/src/openApi/shared/locations/operation.ts
index 3c05b55eee..896879966e 100644
--- a/packages/shared/src/openApi/shared/locations/operation.ts
+++ b/packages/shared/src/openApi/shared/locations/operation.ts
@@ -1,6 +1,7 @@
 import type { StructureLocation } from '@hey-api/codegen-core';
 
 import type { IR } from '../../../ir/types';
+import { operationBaseName } from '../utils/operation';
 
 /**
  * A function that derives path segments from an operation.
@@ -200,5 +201,5 @@ export const OperationPath = {
    * // operation.id: 'getUserById'
    * // Result: ['getUserById']
    */
-  id: (): OperationPathStrategy => (operation) => [operation.id],
+  id: (): OperationPathStrategy => (operation) => [operationBaseName(operation)],
 };
diff --git a/packages/shared/src/openApi/shared/utils/__tests__/operation.test.ts b/packages/shared/src/openApi/shared/utils/__tests__/operation.test.ts
index c26f5dd06b..eefbd04ac0 100644
--- a/packages/shared/src/openApi/shared/utils/__tests__/operation.test.ts
+++ b/packages/shared/src/openApi/shared/utils/__tests__/operation.test.ts
@@ -1,5 +1,30 @@
 import type { Context } from '../../../../ir/context';
-import { operationToId } from '../operation';
+import { toCase } from '../../../../utils/naming/naming';
+import { operationBaseName, operationToId, sanitizeNamespaceIdentifier } from '../operation';
+
+describe('operationBaseName', () => {
+  const operationId = 'RequestOperations_describeHTTPRequest';
+
+  it.each(['camelCase', 'PascalCase', 'snake_case', 'SCREAMING_SNAKE_CASE', 'preserve'] as const)(
+    'returns raw operationId when operation.id was built with output.case=%s',
+    (casing) => {
+      const id = toCase(sanitizeNamespaceIdentifier(operationId), casing);
+      expect(operationBaseName({ id, operationId })).toBe(operationId);
+    },
+  );
+
+  it('falls back to operation.id when operationId is missing', () => {
+    expect(operationBaseName({ id: 'postFoo' })).toBe('postFoo');
+  });
+
+  it('falls back to operation.id when a disambiguation suffix was appended', () => {
+    // operationToId appends a numeric suffix when the sanitized operationId
+    // collides with another operation. The suffix only lives on operation.id
+    // and must be preserved.
+    expect(operationBaseName({ id: 'create2', operationId: 'create_' })).toBe('create2');
+    expect(operationBaseName({ id: 'create3', operationId: 'create__' })).toBe('create3');
+  });
+});
 
 describe('operationToId', () => {
   const scenarios: Array<{
diff --git a/packages/shared/src/openApi/shared/utils/operation.ts b/packages/shared/src/openApi/shared/utils/operation.ts
index 8babf5d122..2b1c365fbe 100644
--- a/packages/shared/src/openApi/shared/utils/operation.ts
+++ b/packages/shared/src/openApi/shared/utils/operation.ts
@@ -1,8 +1,37 @@
 import type { Context } from '../../../ir/context';
 import { createOperationKey } from '../../../ir/operation';
+import type { IROperationObject } from '../../../ir/types';
 import { toCase } from '../../../utils/naming/naming';
 import type { State } from '../types/state';
 
+/**
+ * Returns the best raw string to use as the base for deriving names
+ * (types, SDK method names, etc.) from an operation.
+ *
+ * Prefers the spec's `operationId` verbatim so acronyms and separators
+ * survive `case: 'preserve'`. Falls back to the normalized IR `id` when
+ * no `operationId` is present, or when `operation.id` was disambiguated
+ * (suffix appended) because the sanitized operationId collided — in that
+ * case the disambiguator is carried in `operation.id` and must be kept.
+ *
+ * The comparison is case- and separator-insensitive because `operation.id`
+ * is built via `toCase(sanitized, output.case)` and the target casing is
+ * not available here. Stripping non-alphanumerics and lowercasing both
+ * sides isolates the disambiguation signal (the numeric suffix).
+ */
+export const operationBaseName = (
+  operation: Pick<IROperationObject, 'id' | 'operationId'>,
+): string => {
+  if (!operation.operationId) {
+    return operation.id;
+  }
+
+  const canonical = (value: string) => value.replace(/[^a-zA-Z0-9]/g, '').toLowerCase();
+  return canonical(operation.id) === canonical(operation.operationId)
+    ? operation.operationId
+    : operation.id;
+};
+
 export const httpMethods = [
   'delete',
   'get',
diff --git a/specs/3.1.x/acronym-operationid-preserve.yaml b/specs/3.1.x/acronym-operationid-preserve.yaml
new file mode 100644
index 0000000000..592539a089
--- /dev/null
+++ b/specs/3.1.x/acronym-operationid-preserve.yaml
@@ -0,0 +1,43 @@
+openapi: 3.1.0
+info:
+  title: Acronym Casing Preserve
+  version: 1.0.0
+paths:
+  /requests/{id}:
+    get:
+      operationId: RequestOperations_describeHTTPRequest
+      parameters:
+        - name: id
+          in: path
+          required: true
+          schema:
+            type: string
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/HTTPRequest'
+        '404':
+          description: Not Found
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/HTTPError'
+components:
+  schemas:
+    HTTPRequest:
+      type: object
+      properties:
+        id:
+          type: string
+      required:
+        - id
+    HTTPError:
+      type: object
+      properties:
+        message:
+          type: string
+      required:
+        - message