Reject busy synchronous inference requests

September 17, 2026

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.