Reject busy synchronous inference requests

The rejectIfBusy option lets synchronous Workers AI inference requests fail when capacity is unavailable. Use it when your application should not wait in a capacity queue.

Pass the option as the third argument to the Workers AI binding:

const response = await env.AI.run( "@cf/google/gemma-4-26b-a4b-it", { messages: [{ role: "user", content: "Explain capacity queues." }], }, { rejectIfBusy: true }, );

const response = await env.AI.run( "@cf/google/gemma-4-26b-a4b-it", { messages: [{ role: "user", content: "Explain capacity queues." }], }, { rejectIfBusy: true }, );

For the native REST API, add the option to the request body:

curl --request POST \ --url "https://api.cloudflare.com/client/v4/accounts/$ACCOUNT_ID/ai/run/@cf/google/gemma-4-26b-a4b-it" \ --header "Authorization: Bearer $CLOUDFLARE_API_TOKEN" \ --header "Content-Type: application/json" \ --data '{ "messages": [{ "role": "user", "content": "Explain capacity queues." }], "options": { "rejectIfBusy": true } }'

Refer to Reject busy requests for OpenAI-compatible usage and error behavior.