diff --git a/src/benchmarks/agent-cli/schema.ts b/src/benchmarks/agent-cli/schema.ts
index 57fc926c..bdd69e91 100644
--- a/src/benchmarks/agent-cli/schema.ts
+++ b/src/benchmarks/agent-cli/schema.ts
@@ -1,3 +1,5 @@
+import type { ReasoningEffort } from "../../harness/constants";
+import { ADAPTIVE_REASONING_EFFORT } from "../../harness/constants";
 import type { ValueOf } from "../../internal/guards";
 
 export const ORI_AGENTS = ["pi", "claude", "prime-agent", "omp"] as const;
@@ -22,6 +24,12 @@ export const ORI_REASONING_EFFORTS = [
 
 export type OriReasoningEffort = ValueOf<typeof ORI_REASONING_EFFORTS>;
 
+export function toOriReasoningEffort(
+  effort: ReasoningEffort
+): OriReasoningEffort | undefined {
+  return effort === ADAPTIVE_REASONING_EFFORT ? undefined : effort;
+}
+
 export const AGENT_PACKAGE_PATTERN = /^[A-Za-z0-9@/:._^=+-]+$/;
 
 export function isValidAgentPackage(value: string): boolean {
diff --git a/src/benchmarks/benchmark-config.test.ts b/src/benchmarks/benchmark-config.test.ts
index 4cba901a..4405e1f3 100644
--- a/src/benchmarks/benchmark-config.test.ts
+++ b/src/benchmarks/benchmark-config.test.ts
@@ -47,6 +47,17 @@ describe("benchmark config", () => {
     assertLeft(result);
   });
 
+  it("accepts the explicit auto reasoning effort", () => {
+    const result = parseSchema(BenchmarkRunConfigSchema, {
+      benchmarkId: "gpqa_diamond",
+      model: "openrouter/jev",
+      reasoningEffort: "auto",
+    });
+
+    assertRight(result);
+    expect(result.right.reasoningEffort).toBe("auto");
+  });
+
   it("parses injected benchmark configs with opaque options", () => {
     const result = parseSchema(BenchmarkRunConfigSchema, {
       benchmarkId: "injected_benchmark",
diff --git a/src/benchmarks/deep-swe/solver.ts b/src/benchmarks/deep-swe/solver.ts
index fa8bca00..469f5abf 100644
--- a/src/benchmarks/deep-swe/solver.ts
+++ b/src/benchmarks/deep-swe/solver.ts
@@ -39,7 +39,7 @@ import {
   runAgentCli,
 } from "../agent-cli/runner";
 import type { HarborAgent } from "../agent-cli/schema";
-import { isOriAgent } from "../agent-cli/schema";
+import { isOriAgent, toOriReasoningEffort } from "../agent-cli/schema";
 import type { InferenceOverride } from "../benchmark-config";
 import type { AgentLoopInput } from "../harbor/agent-loop";
 import { AGENT_ENV, probeSystemInfo, runAgentLoop } from "../harbor/agent-loop";
@@ -104,15 +104,25 @@ export function makeDeepSweSolver(
       const task = loadTask(meta.taskId, tasksRoot);
       const agent = opts.agent ?? "mini_swe";
       const cliHarness = isOriAgent(agent) ? getOriHarness(agent) : undefined;
-      const baseCliOpts: AgentCliOpts =
+      const agentReasoningEffort = toOriReasoningEffort(
+        opts.inference.reasoningEffort
+      );
+      const baseCliOpts: AgentCliOpts | undefined =
         opts.agentCli ??
-        definedValues({
-          model: opts.model,
-          apiKey: opts.apiKey,
-          endpointId: opts.endpointId,
-          sessionId: opts.sessionId,
-          agentReasoningEffort: opts.inference.reasoningEffort,
+        (agentReasoningEffort === undefined
+          ? undefined
+          : definedValues({
+              model: opts.model,
+              apiKey: opts.apiKey,
+              endpointId: opts.endpointId,
+              sessionId: opts.sessionId,
+              agentReasoningEffort,
+            }));
+      if (baseCliOpts === undefined) {
+        return yield* new SolverError({
+          message: `deep-swe agent CLI requires a pinned reasoning effort (got "${opts.inference.reasoningEffort}")`,
         });
+      }
       const cliOpts: AgentCliOpts = {
         ...baseCliOpts,
         appendSystemPrompt:
diff --git a/src/benchmarks/search/core/request.test.ts b/src/benchmarks/search/core/request.test.ts
index da276ff8..30aed2fb 100644
--- a/src/benchmarks/search/core/request.test.ts
+++ b/src/benchmarks/search/core/request.test.ts
@@ -196,6 +196,14 @@ describe("buildSearchRequestBody", () => {
     expect(body.temperature).toBe(0);
     expect(body.reasoning).toEqual({ effort: "high" });
   });
+  it("omits reasoning on the wire when effort is auto", () => {
+    const body = buildSearchRequestBody({
+      ...BASE,
+      lane: lane({}),
+      reasoningEffort: "auto",
+    });
+    expect(Object.hasOwn(body, "reasoning")).toBe(false);
+  });
   it("threads the candidate models list and omits it by default", () => {
     const routed = buildSearchRequestBody({
       ...BASE,
diff --git a/src/benchmarks/search/core/request.ts b/src/benchmarks/search/core/request.ts
index c2cf6588..8362daa3 100644
--- a/src/benchmarks/search/core/request.ts
+++ b/src/benchmarks/search/core/request.ts
@@ -9,6 +9,7 @@ import type {
 } from "@openrouter/sdk/models";
 
 import type { CostTier, ReasoningEffort } from "../../../harness/constants";
+import { reasoningRequestFor } from "../../../harness/constants";
 import type { ProviderSort } from "../../../internal/enums";
 import { definedValues } from "../../../internal/guards";
 import { buildAutoRouterPlugin } from "../../../providers/auto-router-plugin";
@@ -127,7 +128,7 @@ export function buildSearchRequestBody(
       models: opts.models === undefined ? undefined : [...opts.models],
       maxOutputTokens: opts.maxOutputTokens,
       temperature: opts.temperature,
-      reasoning: { effort: opts.reasoningEffort },
+      reasoning: reasoningRequestFor(opts.reasoningEffort),
       provider:
         opts.sort !== undefined ||
         opts.providerOrder !== undefined ||
diff --git a/src/benchmarks/swe-atlas/solver.ts b/src/benchmarks/swe-atlas/solver.ts
index a65f2e5a..38d1ceea 100644
--- a/src/benchmarks/swe-atlas/solver.ts
+++ b/src/benchmarks/swe-atlas/solver.ts
@@ -23,7 +23,7 @@ import {
   runAgentCli,
 } from "../agent-cli/runner";
 import type { HarborAgent } from "../agent-cli/schema";
-import { isOriAgent } from "../agent-cli/schema";
+import { isOriAgent, toOriReasoningEffort } from "../agent-cli/schema";
 import type { InferenceOverride } from "../benchmark-config";
 import { AGENT_ENV, probeSystemInfo, runAgentLoop } from "../harbor/agent-loop";
 import {
@@ -105,14 +105,24 @@ export function makeSweAtlasSolver(
       const task = loadTask(meta.taskId, meta.track, tasksRoot);
       const agent = opts.agent ?? "mini_swe";
       const cliHarness = isOriAgent(agent) ? getOriHarness(agent) : undefined;
-      const baseCliOpts: AgentCliOpts =
+      const agentReasoningEffort = toOriReasoningEffort(
+        opts.inference.reasoningEffort
+      );
+      const baseCliOpts: AgentCliOpts | undefined =
         opts.agentCli ??
-        definedValues({
-          model: opts.model,
-          apiKey: opts.apiKey,
-          endpointId: opts.endpointId,
-          agentReasoningEffort: opts.inference.reasoningEffort,
+        (agentReasoningEffort === undefined
+          ? undefined
+          : definedValues({
+              model: opts.model,
+              apiKey: opts.apiKey,
+              endpointId: opts.endpointId,
+              agentReasoningEffort,
+            }));
+      if (baseCliOpts === undefined) {
+        return yield* new SolverError({
+          message: `swe-atlas agent CLI requires a pinned reasoning effort (got "${opts.inference.reasoningEffort}")`,
         });
+      }
       const cliOpts: AgentCliOpts = {
         ...baseCliOpts,
         appendSystemPrompt: joinAgentPrompts(
diff --git a/src/cli/index.test.ts b/src/cli/index.test.ts
index 326bff7b..11086512 100644
--- a/src/cli/index.test.ts
+++ b/src/cli/index.test.ts
@@ -4,6 +4,33 @@ import { buildBenchmarkConfig, parseArgs } from ".";
 describe("bench-harness CLI", () => {
   it("defaults --reasoning-effort to high", () => {
     expect(parseArgs([]).reasoningEffort).toBe("high");
+    expect(parseArgs(["--model", "openai/gpt-5"]).reasoningEffort).toBe("high");
+  });
+
+  it("defaults --reasoning-effort to auto for openrouter/jev", () => {
+    expect(parseArgs(["--model", "openrouter/jev"]).reasoningEffort).toBe(
+      "auto"
+    );
+    expect(parseArgs(["--model", "openrouter/jev:nitro"]).reasoningEffort).toBe(
+      "auto"
+    );
+    expect(
+      parseArgs(["--model", "openrouter/jev", "--reasoning-effort", "high"])
+        .reasoningEffort
+    ).toBe("high");
+    expect(
+      parseArgs(["--model", "openrouter/jev", "--reasoning-effort", "auto"])
+        .reasoningEffort
+    ).toBe("auto");
+  });
+
+  it("rejects --reasoning-effort auto for models without adaptive effort", () => {
+    expect(() =>
+      parseArgs(["--model", "openai/gpt-5", "--reasoning-effort", "auto"])
+    ).toThrow("--reasoning-effort auto is only supported for");
+    expect(() => parseArgs(["--reasoning-effort", "auto"])).toThrow(
+      "--reasoning-effort auto is only supported for"
+    );
   });
 
   it("accepts an explicit --reasoning-effort", () => {
@@ -141,6 +168,33 @@ describe("bench-harness CLI", () => {
     });
   });
 
+  it("does not derive an ori agent reasoning effort from auto", () => {
+    expect(() =>
+      buildBenchmarkConfig({
+        benchmarkId: "terminal_bench",
+        model: "openrouter/jev",
+        panelConfig: undefined,
+        artifactDir: undefined,
+        endpointId: undefined,
+        imageDetail: undefined,
+        reasoningEffort: "auto",
+      })
+    ).toThrow();
+    const config = buildBenchmarkConfig({
+      benchmarkId: "terminal_bench",
+      model: "openrouter/jev",
+      panelConfig: { agentReasoningEffort: "high" },
+      artifactDir: undefined,
+      endpointId: undefined,
+      imageDetail: undefined,
+      reasoningEffort: "auto",
+    });
+    expect(config).toMatchObject({
+      reasoningEffort: "auto",
+      agentReasoningEffort: "high",
+    });
+  });
+
   it("preserves explicit ori agent reasoning effort", () => {
     const config = buildBenchmarkConfig({
       benchmarkId: "terminal_bench",
diff --git a/src/cli/index.ts b/src/cli/index.ts
index 4c9aea8d..cf8487cf 100644
--- a/src/cli/index.ts
+++ b/src/cli/index.ts
@@ -18,11 +18,14 @@ import { DracoPanelConfigSchema } from "../benchmarks/draco/schemas";
 import { benchmarkIds, getBenchmark } from "../benchmarks/registry";
 import type { CostTier, ReasoningEffort } from "../harness/constants";
 import {
+  ADAPTIVE_REASONING_EFFORT,
+  ADAPTIVE_REASONING_EFFORT_MODELS,
   COST_TIERS,
-  DEFAULT_REASONING_EFFORT,
+  defaultReasoningEffortFor,
   ImageDetail,
   IMAGE_DETAIL_VALUES,
   REASONING_EFFORTS,
+  supportsAdaptiveReasoningEffort,
 } from "../harness/constants";
 import { makeProgressReporter } from "../harness/progress";
 import { runHarnessPromise } from "../internal/effect-logger";
@@ -72,7 +75,10 @@ export function parseArgs(argv: readonly string[]): CliArgs {
     resumeId: get("--resume-id"),
     imageDetail: validateImageDetail(get("--image-detail")),
     costTier: validateCostTier(get("--cost-tier")),
-    reasoningEffort: validateReasoningEffort(get("--reasoning-effort")),
+    reasoningEffort: validateReasoningEffort(
+      get("--reasoning-effort"),
+      get("--model")
+    ),
   };
 }
 
@@ -304,15 +310,26 @@ function validateCostTier(raw: string | undefined): CostTier | undefined {
   return raw;
 }
 
-function validateReasoningEffort(raw: string | undefined): ReasoningEffort {
+function validateReasoningEffort(
+  raw: string | undefined,
+  model: string | undefined
+): ReasoningEffort {
   if (raw === undefined) {
-    return DEFAULT_REASONING_EFFORT;
+    return defaultReasoningEffortFor(model);
   }
   if (!isMember(raw, REASONING_EFFORTS)) {
     throw new Error(
       `--reasoning-effort must be one of: ${REASONING_EFFORTS.join(", ")} (got "${raw}")`
     );
   }
+  if (
+    raw === ADAPTIVE_REASONING_EFFORT &&
+    (model === undefined || !supportsAdaptiveReasoningEffort(model))
+  ) {
+    throw new Error(
+      `--reasoning-effort ${ADAPTIVE_REASONING_EFFORT} is only supported for: ${ADAPTIVE_REASONING_EFFORT_MODELS.join(", ")} (got model "${model ?? ""}")`
+    );
+  }
   return raw;
 }
 
@@ -372,6 +389,7 @@ function buildSchemaValidatedConfig(opts: {
     : undefined;
   if (
     optionsSchema !== undefined &&
+    reasoningEffort !== ADAPTIVE_REASONING_EFFORT &&
     Object.hasOwn(optionsSchema.shape, "agentReasoningEffort") &&
     !(
       typeof panelConfig === "object" &&
diff --git a/src/harness/constants.test.ts b/src/harness/constants.test.ts
new file mode 100644
index 00000000..ca6a2e0a
--- /dev/null
+++ b/src/harness/constants.test.ts
@@ -0,0 +1,18 @@
+import { describe, expect, it } from "bun:test";
+
+import { defaultReasoningEffortFor, reasoningRequestFor } from "./constants";
+
+describe("reasoning effort constants", () => {
+  it("defaults openrouter/jev to auto and everything else to high", () => {
+    expect(defaultReasoningEffortFor("openrouter/jev")).toBe("auto");
+    expect(defaultReasoningEffortFor("openrouter/jev:nitro")).toBe("auto");
+    expect(defaultReasoningEffortFor("openai/gpt-5")).toBe("high");
+    expect(defaultReasoningEffortFor(undefined)).toBe("high");
+  });
+
+  it("maps auto to no reasoning object and pins every other effort", () => {
+    expect(reasoningRequestFor("auto")).toBeUndefined();
+    expect(reasoningRequestFor("high")).toEqual({ effort: "high" });
+    expect(reasoningRequestFor("none")).toEqual({ effort: "none" });
+  });
+});
diff --git a/src/harness/constants.ts b/src/harness/constants.ts
index f6bf2ec8..614d545f 100644
--- a/src/harness/constants.ts
+++ b/src/harness/constants.ts
@@ -1,6 +1,8 @@
 import type { ValueOf } from "../internal/guards";
 
-export const REASONING_EFFORTS = [
+export const ADAPTIVE_REASONING_EFFORT = "auto";
+
+export const PINNED_REASONING_EFFORTS = [
   "xhigh",
   "high",
   "medium",
@@ -9,10 +11,38 @@ export const REASONING_EFFORTS = [
   "none",
 ] as const;
 
+export type PinnedReasoningEffort = ValueOf<typeof PINNED_REASONING_EFFORTS>;
+
+export const REASONING_EFFORTS = [
+  ...PINNED_REASONING_EFFORTS,
+  ADAPTIVE_REASONING_EFFORT,
+] as const;
+
 export type ReasoningEffort = ValueOf<typeof REASONING_EFFORTS>;
 
 export const DEFAULT_REASONING_EFFORT: ReasoningEffort = "high";
 
+export const ADAPTIVE_REASONING_EFFORT_MODELS = ["openrouter/jev"] as const;
+
+export function supportsAdaptiveReasoningEffort(model: string): boolean {
+  const baseModel = model.split(":")[0];
+  return ADAPTIVE_REASONING_EFFORT_MODELS.some((slug) => slug === baseModel);
+}
+
+export function defaultReasoningEffortFor(
+  model: string | undefined
+): ReasoningEffort {
+  return model !== undefined && supportsAdaptiveReasoningEffort(model)
+    ? ADAPTIVE_REASONING_EFFORT
+    : DEFAULT_REASONING_EFFORT;
+}
+
+export function reasoningRequestFor(
+  effort: ReasoningEffort
+): { readonly effort: PinnedReasoningEffort } | undefined {
+  return effort === ADAPTIVE_REASONING_EFFORT ? undefined : { effort };
+}
+
 export const COST_TIERS = ["low", "medium", "high", "xhigh", "max"] as const;
 
 export type CostTier = ValueOf<typeof COST_TIERS>;
diff --git a/src/judge/judge.ts b/src/judge/judge.ts
index 89499dd6..f134ffa8 100644
--- a/src/judge/judge.ts
+++ b/src/judge/judge.ts
@@ -6,6 +6,7 @@ import type { Effect } from "effect/Effect";
 import { fail, flatMap, mapError, succeed } from "effect/Effect";
 
 import type { ReasoningEffort } from "../harness/constants";
+import { reasoningRequestFor } from "../harness/constants";
 import type { ModelUsage } from "../harness/core";
 import { ModelError } from "../harness/core";
 import { Either } from "../internal/either";
@@ -67,7 +68,7 @@ export function judgeCall<T>(
     text,
     instructions: spec.instructions,
     temperature: config.temperature,
-    reasoning: { effort: config.reasoningEffort },
+    reasoning: reasoningRequestFor(config.reasoningEffort),
   });
   const sendOptions = definedValues({
     timeoutMs: config.timeoutMs ?? DEFAULT_JUDGE_TIMEOUT_MS,
diff --git a/src/providers/responses-model.test.ts b/src/providers/responses-model.test.ts
index e3dd04e2..117ef46a 100644
--- a/src/providers/responses-model.test.ts
+++ b/src/providers/responses-model.test.ts
@@ -360,6 +360,26 @@ describe("responses-model", () => {
     expect(captured.value?.body["provider"]).toBeUndefined();
     expect(captured.value?.headers["x-or-endpoint-id"]).toBe("endpoint-1");
   });
+  it("omits reasoning on the wire when effort is auto", async () => {
+    const captured: {
+      value: CapturedRequest | undefined;
+    } = { value: undefined };
+    restore = installFetchStub(await readStreamFixture(), 200, captured);
+    const layer = makeResponsesModelLayer({
+      model: "openrouter/jev",
+      apiKey: "sk-test",
+      retry: { baseDelayMs: 0, maxRetries: 0 },
+    });
+    const exit = await runPromiseExit(
+      gen(function* run() {
+        const model = yield* ResponsesModel;
+        return yield* model.generate([], { reasoningEffort: "auto" });
+      }).pipe(provide(layer.pipe(layerProvide(FetchHttpClient.layer))))
+    );
+    assertSuccess(exit);
+    expect(captured.value).toBeDefined();
+    expect(Object.hasOwn(captured.value?.body ?? {}, "reasoning")).toBe(false);
+  });
   it("sends provider.only with fallbacks disabled on pinned runs", async () => {
     const captured: {
       value: CapturedRequest | undefined;
diff --git a/src/providers/responses-model.ts b/src/providers/responses-model.ts
index b558d63d..1972ca90 100644
--- a/src/providers/responses-model.ts
+++ b/src/providers/responses-model.ts
@@ -20,6 +20,7 @@ import {
 import type { Layer } from "effect/Layer";
 import { effect, provide } from "effect/Layer";
 
+import { reasoningRequestFor } from "../harness/constants";
 import type { ModelUsage } from "../harness/core";
 import { ModelError } from "../harness/core";
 import type { GenerateConfig } from "../harness/model";
@@ -185,8 +186,8 @@ export function generate(
           ? [...genConfig.tools]
           : undefined,
     }),
-    reasoning: { effort: genConfig.reasoningEffort },
     ...definedValues({
+      reasoning: reasoningRequestFor(genConfig.reasoningEffort),
       provider: sendProvider ? providerPreferences : undefined,
     }),
     ...definedValues({