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 7c34bb73559..cbb797c807b 100644
--- a/packages/effect/src/unstable/httpapi/OpenApi.ts
+++ b/packages/effect/src/unstable/httpapi/OpenApi.ts
@@ -224,6 +224,25 @@ 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)) {
+      Object.defineProperty(out, key, {
+        value: cloneOpenAPISpec((value as Record<string, unknown>)[key]),
+        enumerable: true,
+        configurable: true,
+        writable: true
+      })
+    }
+    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
@@ -273,7 +292,7 @@ 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",
@@ -665,7 +684,7 @@ function fromApiWith<Id extends string, Groups extends HttpApiGroup.Constraint>(
 
   cache.set(api, spec)
 
-  return spec
+  return cloneOpenAPISpec(spec)
 }
 
 type ResponseBodies = Map<
diff --git a/packages/effect/test/unstable/httpapi/OpenApi.test.ts b/packages/effect/test/unstable/httpapi/OpenApi.test.ts
index 72e2f2e97fc..0e5830e3167 100644
--- a/packages/effect/test/unstable/httpapi/OpenApi.test.ts
+++ b/packages/effect/test/unstable/httpapi/OpenApi.test.ts
@@ -70,6 +70,33 @@ 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("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"