diff --git a/.changeset/optional-anonymous-security.md b/.changeset/optional-anonymous-security.md
new file mode 100644
index 000000000..ffbc633ed
--- /dev/null
+++ b/.changeset/optional-anonymous-security.md
@@ -0,0 +1,7 @@
+---
+'fets': patch
+---
+
+Make client auth params optional when an operation's `security` array includes an anonymous alternative (`{}`)
+
+OpenAPI allows listing an empty security requirement beside authenticated schemes so callers may omit credentials. The client types previously still required auth params whenever any scheme was present. Empty `{}` entries are now detected and the corresponding auth params become optional.
diff --git a/packages/fets/src/client/types.ts b/packages/fets/src/client/types.ts
index 1af68c972..819be870c 100644
--- a/packages/fets/src/client/types.ts
+++ b/packages/fets/src/client/types.ts
@@ -681,12 +681,25 @@ export type SecuritySchemeName<T extends { security: { [key: string]: any }[] }>
   T['security']
 >[number];
 
+type HasAnonymousSecurityAlternative<T extends { security: { [key: string]: any }[] }> =
+  true extends (
+    T['security'][number] extends infer TRequirement
+      ? TRequirement extends unknown
+        ? keyof TRequirement extends never
+          ? true
+          : false
+        : false
+      : false
+  )
+    ? true
+    : false;
+
 export type OASSecurityParams<TSecurityScheme> = BasicAuthParams<TSecurityScheme> &
   BearerAuthParams<TSecurityScheme> &
   ApiKeyAuthParams<TSecurityScheme> &
   OAuth2AuthParams<TSecurityScheme>;
 
-export type OASSecurityParamsBySecurityRef<TOAS, TSecurityObj> = TSecurityObj extends {
+type OASSecurityParamsBySecurityRefBase<TOAS, TSecurityObj> = TSecurityObj extends {
   security: { [key: string]: any }[];
 }
   ? TOAS extends
@@ -729,3 +742,11 @@ export type OASSecurityParamsBySecurityRef<TOAS, TSecurityObj> = TSecurityObj ex
             }>
           : {}
   : {};
+
+export type OASSecurityParamsBySecurityRef<TOAS, TSecurityObj> = TSecurityObj extends {
+  security: { [key: string]: any }[];
+}
+  ? HasAnonymousSecurityAlternative<TSecurityObj> extends true
+    ? DeepPartial<OASSecurityParamsBySecurityRefBase<TOAS, TSecurityObj>>
+    : OASSecurityParamsBySecurityRefBase<TOAS, TSecurityObj>
+  : {};
diff --git a/packages/fets/tests/client/fixtures/example-optional-apiKey-header-oas.ts b/packages/fets/tests/client/fixtures/example-optional-apiKey-header-oas.ts
new file mode 100644
index 000000000..d01526b7f
--- /dev/null
+++ b/packages/fets/tests/client/fixtures/example-optional-apiKey-header-oas.ts
@@ -0,0 +1,74 @@
+export default {
+  components: {
+    securitySchemes: {
+      apiKey: {
+        type: 'apiKey',
+        name: 'x-api-key',
+        in: 'header',
+      },
+    },
+    schemas: {
+      UnauthorizedResponse: {
+        properties: {
+          message: {
+            type: 'string',
+          },
+        },
+        type: 'object',
+        additionalProperties: false,
+        required: ['message'],
+      },
+      User: {
+        properties: {
+          id: {
+            type: 'integer',
+          },
+          name: {
+            type: 'string',
+          },
+        },
+        type: 'object',
+        additionalProperties: false,
+        required: ['id', 'name'],
+      },
+    },
+  },
+  paths: {
+    '/me': {
+      get: {
+        operationId: 'getMe',
+        // Empty object = anonymous alternative; auth is optional
+        security: [
+          {},
+          {
+            apiKey: [],
+          },
+        ],
+        responses: {
+          '200': {
+            content: {
+              'application/json': {
+                schema: {
+                  $ref: '#/components/schemas/User',
+                },
+              },
+            },
+            description: 'OK',
+          },
+          401: {
+            content: {
+              'application/json': {
+                schema: {
+                  $ref: '#/components/schemas/UnauthorizedResponse',
+                },
+              },
+            },
+            description: 'Unauthorized',
+          },
+        },
+        summary: 'get me',
+        tags: ['User'],
+      },
+    },
+  },
+} as const;
diff --git a/packages/fets/tests/client/optional-apiKey-test.ts b/packages/fets/tests/client/optional-apiKey-test.ts
new file mode 100644
index 000000000..317a8c8e8
--- /dev/null
+++ b/packages/fets/tests/client/optional-apiKey-test.ts
@@ -0,0 +1,22 @@
+import { createClient, type NormalizeOAS } from '../../src';
+
+type NormalizedOAS = NormalizeOAS<
+  (typeof import('./fixtures/example-optional-apiKey-header-oas'))['default']
+>;
+const client = createClient<NormalizedOAS>({});
+
+// Auth is optional because security includes an anonymous `{}` alternative
+await client['/me'].get();
+
+const res = await client['/me'].get({
+  headers: {
+    'x-api-key': '123',
+  },
+});
+
+if (!res.ok) {
+  const errData = await res.json();
+  throw new Error(errData.message);
+}
+const data = await res.json();
+console.info(`User ${data.id}: ${data.name}`);