diff --git a/.changeset/fix-openapi-from-api-cache-copy.md b/.changeset/fix-openapi-from-api-cache-copy.md
new file mode 100644
index 00000000000..68a5c04f448
--- /dev/null
+++ b/.changeset/fix-openapi-from-api-cache-copy.md
@@ -0,0 +1,5 @@
+---
+"effect": patch
+---
+
+Return fresh OpenAPI specs from cached `OpenApi.fromApi` calls.
diff --git a/packages/effect/src/unstable/httpapi/OpenApi.ts b/packages/effect/src/unstable/httpapi/OpenApi.ts
index 3b119b4188d..c7ff5bff44f 100644
--- a/packages/effect/src/unstable/httpapi/OpenApi.ts
+++ b/packages/effect/src/unstable/httpapi/OpenApi.ts
@@ -227,6 +227,20 @@ const compileSchemas: CompileSchemas = (asts) =>
     )
   )
 
+const cloneOpenAPISpec = <A>(value: A): A => {
+  if (Array.isArray(value)) {
+    return value.map(cloneOpenAPISpec) as A
+  }
+  if (value !== null && typeof value === "object") {
+    const out: Record<string, unknown> = {}
+    for (const key of Object.keys(value)) {
+      InternalRecord.assignProperty(out, key, cloneOpenAPISpec((value as Record<string, unknown>)[key]))
+    }
+    return out as A
+  }
+  return value
+}
+
 /**
  * This function checks if a given tag exists within the provided context. If
  * the tag is present, it retrieves the associated value and applies the given
@@ -276,7 +290,7 @@ function fromApiWith<Id extends string, Groups extends HttpApiGroup.Constraint>(
 ): OpenAPISpec {
   const cached = cache.get(api)
   if (cached !== undefined) {
-    return cached
+    return cloneOpenAPISpec(cached)
   }
   let spec: OpenAPISpec = {
     openapi: "3.1.0",
@@ -685,7 +699,7 @@ function fromApiWith<Id extends string, Groups extends HttpApiGroup.Constraint>(
     spec = transformFn(spec) as OpenAPISpec
   })
 
-  cache.set(api, spec)
+  cache.set(api, cloneOpenAPISpec(spec))
 
   return spec
 }
diff --git a/packages/effect/test/unstable/httpapi/OpenApi.test.ts b/packages/effect/test/unstable/httpapi/OpenApi.test.ts
index b1d1b88030b..c0de5e47d22 100644
--- a/packages/effect/test/unstable/httpapi/OpenApi.test.ts
+++ b/packages/effect/test/unstable/httpapi/OpenApi.test.ts
@@ -70,6 +70,45 @@ const makeSecurityApi = (
   )
 
 describe("OpenApi", () => {
+  it("returns fresh spec instances when using the cache", () => {
+    const Api = HttpApi.make("Api").add(
+      HttpApiGroup.make("test").add(
+        HttpApiEndpoint.get("get", "/resource")
+      )
+    )
+
+    const first = OpenApi.fromApi(Api)
+    first.info.title = "mutated"
+    first.paths["/resource"]!.get!.summary = "mutated"
+
+    const second = OpenApi.fromApi(Api)
+
+    assert.notStrictEqual(first, second)
+    assert.notStrictEqual(first.info, second.info)
+    assert.notStrictEqual(first.paths["/resource"]!.get, second.paths["/resource"]!.get)
+    assert.strictEqual(second.info.title, "Api")
+    assert.isUndefined(second.paths["/resource"]!.get!.summary)
+
+    second.info.title = "mutated again"
+    second.paths["/resource"]!.get!.summary = "mutated again"
+    const third = OpenApi.fromApi(Api)
+
+    assert.strictEqual(third.info.title, "Api")
+    assert.isUndefined(third.paths["/resource"]!.get!.summary)
+  })
+
+  it("isolates the cached spec from external override mutations", () => {
+    const info = { title: "Api", version: "1.0.0" }
+    const Api = HttpApi.make("Api").annotate(OpenApi.Override, { info })
+
+    OpenApi.fromApi(Api)
+    info.title = "mutated"
+
+    const cached = OpenApi.fromApi(Api)
+
+    assert.strictEqual(cached.info.title, "Api")
+  })
+
   it("preserves every declared payload content type for normalized equivalents", () => {
     const profileA = "Application/Vnd.Effect+JSON; Profile=A"
     const profileB = "application/vnd.effect+json; profile=b"
diff --git a/packages/effect/test/unstable/httpapi/OpenApiRepresentation.test.ts b/packages/effect/test/unstable/httpapi/OpenApiRepresentation.test.ts
index fb9b62c6b54..b7bfe385672 100644
--- a/packages/effect/test/unstable/httpapi/OpenApiRepresentation.test.ts
+++ b/packages/effect/test/unstable/httpapi/OpenApiRepresentation.test.ts
@@ -110,7 +110,7 @@ describe("OpenApi representation v2 consumer", () => {
     )
   })
 
-  it("shares definitions and caches by API identity", () => {
+  it("shares definitions and returns cached copies by API identity", () => {
     const Shared = Schema.Struct({ value: Schema.FiniteFromString }).annotate({ identifier: "Shared" })
     const Api = HttpApi.make("Api").add(
       HttpApiGroup.make("test").add(
@@ -122,8 +122,10 @@ describe("OpenApi representation v2 consumer", () => {
     )
 
     const first = OpenApi.fromApi(Api)
+    const second = OpenApi.fromApi(Api)
 
-    assert.strictEqual(OpenApi.fromApi(Api), first)
+    assert.notStrictEqual(second, first)
+    assert.deepStrictEqual(second, first)
     assert.deepStrictEqual(first.components.schemas.Shared, {
       type: "object",
       properties: { value: { type: "string" } },