Anthropic Claude API Webhook Integration Guide

Does the Claude API support webhooks?

Short answer: no, not natively. The Anthropic Claude API (and compatible gateways like SubToAPI) is a synchronous request/response API — you send a prompt, you get a completion back in the same HTTP call, or as a stream of chunks. There's no mechanism where Claude itself pushes a notification to a URL when something happens, the way Stripe or GitHub fire webhooks on events.

What developers usually mean when they search for "Claude API webhook integration" is one of two things: (1) triggering a Claude call from an incoming webhook — Slack commands, form submissions, GitHub events, Stripe events — or (2) getting notified asynchronously when a long-running Claude job finishes, because the caller doesn't want to hold an HTTP connection open. Both are entirely achievable, but you build the webhook layer yourself around the Claude request/response cycle. This article covers the patterns that actually work in production.

Pattern 1: Incoming webhook triggers a Claude call

This is the most common case. A third-party service calls your endpoint, you extract the payload, send it to Claude, and respond — either synchronously (if the webhook sender waits) or by replying to a callback URL the sender gives you.

// Example: Slack slash command triggers a Claude summary
app.post("/webhooks/slack", async (req, res) => {
  const { text, response_url } = req.body;

  // Acknowledge immediately — Slack times out after 3s
  res.status(200).json({ response_type: "ephemeral", text: "Working on it..." });

  const completion = await fetch("https://api.subtoapi.app/v1/messages", {
    method: "POST",
    headers: {
      "Authorization": `Bearer ${process.env.SUBTOAPI_KEY}`,
      "Content-Type": "application/json"
    },
    body: JSON.stringify({
      model: "claude-sonnet-4",
      max_tokens: 500,
      messages: [{ role: "user", content: `Summarize: ${text}` }]
    })
  });

  const data = await completion.json();

  // Reply to Slack's own webhook URL — this IS a webhook, just not Claude's
  await fetch(response_url, {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({ text: data.content[0].text })
  });
});

The key insight: you're combining two webhook-adjacent concepts — an inbound webhook (Slack calling you) and an outbound callback (you calling Slack back) — with a plain synchronous Claude request in the middle. Claude never talks to a URL directly.

Pattern 2: Queue + outgoing webhook for long jobs

If the Claude call is expensive (large document analysis, multi-step tool use, batch-style work) and you don't want the original caller blocked, build a job queue and fire your own webhook when it's done.

// 1. Accept the job, return a job ID immediately
app.post("/jobs", async (req, res) => {
  const jobId = crypto.randomUUID();
  await queue.add("claude-job", { jobId, payload: req.body });
  res.status(202).json({ job_id: jobId, status: "queued" });
});

// 2. Worker processes the job
queue.process("claude-job", async (job) => {
  const { jobId, payload } = job.data;

  const response = await fetch("https://api.subtoapi.app/v1/messages", {
    method: "POST",
    headers: {
      "Authorization": `Bearer ${process.env.SUBTOAPI_KEY}`,
      "Content-Type": "application/json"
    },
    body: JSON.stringify({
      model: "claude-sonnet-4",
      max_tokens: 2000,
      messages: payload.messages
    })
  });

  const result = await response.json();

  // 3. Fire your own outgoing webhook to the caller's callback URL
  await fetch(payload.callback_url, {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({ job_id: jobId, status: "completed", result })
  });
});

This is the pattern that most closely matches "webhook integration" for LLM APIs in general — you're building the async notification layer because Claude's API won't do it for you.

Streaming vs webhooks — use the right one

If you need live, token-by-token output while the user waits, that's a job for streaming, not webhooks. Don't build a webhook polling loop for something you can stream directly over a single HTTP connection with server-sent events. See /docs/streaming for the implementation, and /docs/messages for the base request format. Webhooks are for decoupling the caller from the worker — streaming is for real-time delivery to a still-connected caller. They solve different problems and are sometimes combined: stream internally to your worker, then webhook a final summary once streaming completes.

Securing your webhook endpoints

Since you're the one building the webhook layer, you're also responsible for securing it:

• Verify signatures on inbound webhooks (Slack, GitHub, Stripe all sign payloads with HMAC — check these before you spend a Claude call on untrusted input).
• Make handlers idempotent. Webhook senders retry on timeout; don't double-charge a Claude call for the same event. Dedupe on an event ID.
• Keep your Claude API key server-side only. Never expose it in a webhook handler that's reachable from client-side code — route all calls through your backend, using scoped application keys (sub_live_...) rather than your raw Anthropic account credentials. This also gives you per-key usage visibility if something misbehaves.
• Set a timeout and fallback for the Claude call inside the handler so a slow response doesn't cascade into webhook retries from the sender.

If you're managing multiple webhook-triggered integrations across a team — Slack bots, support ticket enrichment, CI pipeline annotations — a dashboard that tracks which API key is driving which integration pays off fast when something starts erroring. SubToAPI issues separate application keys per integration with usage metadata per key, so you can see exactly which webhook handler is burning tokens. Get started at /signup or check /docs/quickstart for the first request.

Questions

Does Anthropic's Claude API have native webhook support? No. Claude's API is purely request/response (including streamed responses over a single connection). Any webhook behavior — inbound triggers or outbound notifications — is something you implement in your own application layer around the API calls.

How do I know when a long Claude request finishes without polling? Use a queue-and-callback pattern: accept the job, return a job ID immediately, process it in a background worker, then POST the result to a callback URL the caller provided. That callback POST is your outgoing webhook.

Can I trigger Claude from Stripe, GitHub, or Slack webhooks? Yes — this is the most common pattern. Verify the incoming webhook's signature, extract the relevant data, send it to Claude via /docs/messages, and either respond synchronously or reply through the sender's own callback mechanism (like Slack's response_url).