Workflows, Workers - Stream Workflow instance events in your Worker or via the API with .subscribe()

<p>You can now stream Workflow instance events via <code>WorkflowInstance.subscribe()</code> and the <code>GET /subscribe</code> API endpoint. Workers and HTTP clients can react to <a href="https://developers.cloudflare.com/workflows/build/events-and-parameters/">workflow</a> and <a href="https://developers.cloudflare.com/workflows/build/step-context/#workflowstepcontext">step</a> events, including attempts, sleeps, waits, and rollbacks, without polling for instance status.</p> <p>A subscription first streams the entire event history of the Workflow instance. After streaming past events, the subscription waits for new events as the instance runs. You can use <code>filter</code> to receive only specific event types or <code>cursor</code> to start a subscription at a specific event.</p> <p>Use <code>.subscribe()</code> to update Workflow status in user-facing dashboards, send notifications when steps complete, or trigger follow-up work for specific events.</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"> instance</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">MY_WORKFLOW</span><span class="nb-shiki-140thh">.</span><span class="nb-shiki-1t8gfj">get</span><span class="nb-shiki-140thh">(</span><span class="nb-shiki-mdbnqw">"report-123"</span><span class="nb-shiki-140thh">);</span></span> <span class="line"></span> <span class="line"><span class="nb-shiki-1itgoe">using</span><span class="nb-shiki-dzsirb"> subscription</span><span class="nb-shiki-1itgoe"> =</span><span class="nb-shiki-1itgoe"> await</span><span class="nb-shiki-140thh"> instance.</span><span class="nb-shiki-1t8gfj">subscribe</span><span class="nb-shiki-140thh">();</span></span> <span class="line"></span> <span class="line"><span class="nb-shiki-1itgoe">while</span><span class="nb-shiki-140thh"> (</span><span class="nb-shiki-dzsirb">true</span><span class="nb-shiki-140thh">) {</span></span> <span class="line"><span class="nb-shiki-1itgoe"> const</span><span class="nb-shiki-140thh"> { </span><span class="nb-shiki-dzsirb">value</span><span class="nb-shiki-140thh">, </span><span class="nb-shiki-dzsirb">done</span><span class="nb-shiki-140thh"> } </span><span class="nb-shiki-1itgoe">=</span><span class="nb-shiki-1itgoe"> await</span><span class="nb-shiki-140thh"> subscription.</span><span class="nb-shiki-1t8gfj">next</span><span class="nb-shiki-140thh">();</span></span> <span class="line"><span class="nb-shiki-1itgoe"> if</span><span class="nb-shiki-140thh"> (done) {</span></span> <span class="line"><span class="nb-shiki-1itgoe"> break</span><span class="nb-shiki-140thh">;</span></span> <span class="line"><span class="nb-shiki-140thh"> }</span></span> <span class="line"></span> <span class="line"><span class="nb-shiki-140thh"> console.</span><span class="nb-shiki-1t8gfj">log</span><span class="nb-shiki-140thh">(value.type, value);</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"> instance</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">MY_WORKFLOW</span><span class="nb-shiki-140thh">.</span><span class="nb-shiki-1t8gfj">get</span><span class="nb-shiki-140thh">(</span><span class="nb-shiki-mdbnqw">"report-123"</span><span class="nb-shiki-140thh">);</span></span> <span class="line"></span> <span class="line"><span class="nb-shiki-1itgoe">using</span><span class="nb-shiki-dzsirb"> subscription</span><span class="nb-shiki-1itgoe"> =</span><span class="nb-shiki-1itgoe"> await</span><span class="nb-shiki-140thh"> instance.</span><span class="nb-shiki-1t8gfj">subscribe</span><span class="nb-shiki-140thh">();</span></span> <span class="line"></span> <span class="line"><span class="nb-shiki-1itgoe">while</span><span class="nb-shiki-140thh"> (</span><span class="nb-shiki-dzsirb">true</span><span class="nb-shiki-140thh">) {</span></span> <span class="line"><span class="nb-shiki-1itgoe"> const</span><span class="nb-shiki-140thh"> { </span><span class="nb-shiki-dzsirb">value</span><span class="nb-shiki-140thh">, </span><span class="nb-shiki-dzsirb">done</span><span class="nb-shiki-140thh"> } </span><span class="nb-shiki-1itgoe">=</span><span class="nb-shiki-1itgoe"> await</span><span class="nb-shiki-140thh"> subscription.</span><span class="nb-shiki-1t8gfj">next</span><span class="nb-shiki-140thh">();</span></span> <span class="line"><span class="nb-shiki-1itgoe"> if</span><span class="nb-shiki-140thh"> (done) {</span></span> <span class="line"><span class="nb-shiki-1itgoe"> break</span><span class="nb-shiki-140thh">;</span></span> <span class="line"><span class="nb-shiki-140thh"> }</span></span> <span class="line"></span> <span class="line"><span class="nb-shiki-140thh"> console.</span><span class="nb-shiki-1t8gfj">log</span><span class="nb-shiki-140thh">(value.type, value);</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 event types, available fields, and subscription options, refer to <a href="https://developers.cloudflare.com/workflows/build/subscribe-to-instance-events/">Subscribe to events</a>.</p>