Workers AI - Reject busy synchronous inference requests

<p>The <code>rejectIfBusy</code> option lets synchronous Workers AI inference requests fail when capacity is unavailable. Use it when your application should not wait in a capacity queue.</p> <p>Pass the option as the third argument to the Workers AI binding:</p> <div><div data-nb-tabs data-nb-sync-key="workersExamples" class><div class="relative flex border-b border-border" role="tablist" data-nb-tabs-list><span class="bg-primary pointer-events-none absolute -bottom-px h-0.5 rounded-t-sm transition-[left,width] duration-200 ease-out" data-nb-tabs-indicator aria-hidden="true"></span></div><div class="mt-3"><div role="tabpanel" data-nb-tabs-content data-nb-tab-label="JavaScript" class><figure class="nb-code-figure" data-nb-lang="js"><pre class="astro-code astro-code-themes github-light github-dark nb-shiki-c6xiwz" tabindex="0" data-language="js" data-nb-lang="js"><code><span class="line"><span class="nb-shiki-1itgoe">const</span><span class="nb-shiki-dzsirb"> response</span><span class="nb-shiki-1itgoe"> =</span><span class="nb-shiki-1itgoe"> await</span><span class="nb-shiki-140thh"> env.</span><span class="nb-shiki-dzsirb">AI</span><span class="nb-shiki-140thh">.</span><span class="nb-shiki-1t8gfj">run</span><span class="nb-shiki-140thh">(</span></span> <span class="line"><span class="nb-shiki-mdbnqw"> "@cf/google/gemma-4-26b-a4b-it"</span><span class="nb-shiki-140thh">,</span></span> <span class="line"><span class="nb-shiki-140thh"> {</span></span> <span class="line"><span class="nb-shiki-140thh"> messages: [{ role: </span><span class="nb-shiki-mdbnqw">"user"</span><span class="nb-shiki-140thh">, content: </span><span class="nb-shiki-mdbnqw">"Explain capacity queues."</span><span class="nb-shiki-140thh"> }],</span></span> <span class="line"><span class="nb-shiki-140thh"> },</span></span> <span class="line"><span class="nb-shiki-140thh"> { rejectIfBusy: </span><span class="nb-shiki-dzsirb">true</span><span class="nb-shiki-140thh"> },</span></span> <span class="line"><span class="nb-shiki-140thh">);</span></span></code></pre></figure></div><div role="tabpanel" data-nb-tabs-content data-nb-tab-label="TypeScript" class><figure class="nb-code-figure" data-nb-lang="ts"><pre class="astro-code astro-code-themes github-light github-dark nb-shiki-c6xiwz" tabindex="0" data-language="ts" data-nb-lang="ts"><code><span class="line"><span class="nb-shiki-1itgoe">const</span><span class="nb-shiki-dzsirb"> response</span><span class="nb-shiki-1itgoe"> =</span><span class="nb-shiki-1itgoe"> await</span><span class="nb-shiki-140thh"> env.</span><span class="nb-shiki-dzsirb">AI</span><span class="nb-shiki-140thh">.</span><span class="nb-shiki-1t8gfj">run</span><span class="nb-shiki-140thh">(</span></span> <span class="line"><span class="nb-shiki-mdbnqw"> "@cf/google/gemma-4-26b-a4b-it"</span><span class="nb-shiki-140thh">,</span></span> <span class="line"><span class="nb-shiki-140thh"> {</span></span> <span class="line"><span class="nb-shiki-140thh"> messages: [{ role: </span><span class="nb-shiki-mdbnqw">"user"</span><span class="nb-shiki-140thh">, content: </span><span class="nb-shiki-mdbnqw">"Explain capacity queues."</span><span class="nb-shiki-140thh"> }],</span></span> <span class="line"><span class="nb-shiki-140thh"> },</span></span> <span class="line"><span class="nb-shiki-140thh"> { rejectIfBusy: </span><span class="nb-shiki-dzsirb">true</span><span class="nb-shiki-140thh"> },</span></span> <span class="line"><span class="nb-shiki-140thh">);</span></span></code></pre></figure></div></div></div><script type="module" src="https://developers.cloudflare.com/home/runner/work/cloudflare-docs/cloudflare-docs/src/components/ui/tabs/Tabs.astro?astro&type=script&index=0&lang.ts"></script></div> <p>For the native REST API, add the option to the request body:</p> <figure class="nb-code-figure" data-nb-lang="bash"><pre class="astro-code astro-code-themes github-light github-dark nb-shiki-c6xiwz" tabindex="0" data-language="bash" data-nb-lang="bash"><code><span class="line"><span class="nb-shiki-1t8gfj">curl</span><span class="nb-shiki-dzsirb"> --request</span><span class="nb-shiki-mdbnqw"> POST</span><span class="nb-shiki-dzsirb"> \</span></span> <span class="line"><span class="nb-shiki-dzsirb"> --url</span><span class="nb-shiki-mdbnqw"> "https://api.cloudflare.com/client/v4/accounts/</span><span class="nb-shiki-140thh">$ACCOUNT_ID</span><span class="nb-shiki-mdbnqw">/ai/run/@cf/google/gemma-4-26b-a4b-it"</span><span class="nb-shiki-dzsirb"> \</span></span> <span class="line"><span class="nb-shiki-dzsirb"> --header</span><span class="nb-shiki-mdbnqw"> "Authorization: Bearer </span><span class="nb-shiki-140thh">$CLOUDFLARE_API_TOKEN</span><span class="nb-shiki-mdbnqw">"</span><span class="nb-shiki-dzsirb"> \</span></span> <span class="line"><span class="nb-shiki-dzsirb"> --header</span><span class="nb-shiki-mdbnqw"> "Content-Type: application/json"</span><span class="nb-shiki-dzsirb"> \</span></span> <span class="line"><span class="nb-shiki-dzsirb"> --data</span><span class="nb-shiki-mdbnqw"> '{</span></span> <span class="line"><span class="nb-shiki-mdbnqw"> "messages": [{ "role": "user", "content": "Explain capacity queues." }],</span></span> <span class="line"><span class="nb-shiki-mdbnqw"> "options": { "rejectIfBusy": true }</span></span> <span class="line"><span class="nb-shiki-mdbnqw"> }'</span></span></code></pre></figure> <p>Refer to <a href="https://developers.cloudflare.com/workers-ai/features/reject-if-busy/">Reject busy requests</a> for OpenAI-compatible usage and error behavior.</p>