How to Retry Failed Claude API Requests

When a Claude API request fails, the right response depends entirely on why it failed. Some errors mean "wait and try again," others mean "fix your request before you try again," and a few mean "don't retry at all." Retrying blindly can waste money on duplicate completions, trigger rate limits harder, or mask a real bug in your integration.

The short answer: retry on 429, 500, 502, 503, 504, and network/timeout errors using exponential backoff with jitter, cap your attempts at 3–5, and never retry on 400, 401, or 403. The rest of this article walks through how to implement that correctly, including code you can drop into a Node.js or Python client.

Which errors are retryable

Claude API errors fall into three buckets:

Retryable (transient):

• 429 Too Many Requests — you hit a rate limit, retry after backing off
• 500 Internal Server Error — temporary server-side issue
• 502 / 503 / 504 — gateway/upstream unavailability
• Network errors — connection reset, DNS failure, socket timeout

Not retryable (client-side, fix before resending):

• 400 Bad Request — malformed request body, invalid parameters
• 401 Unauthorized — missing or invalid API key
• 403 Forbidden — valid key, insufficient permission
• 404 Not Found — wrong endpoint or model name

Situational:

• Request timeouts on very long streaming responses — retryable, but check whether the stream already delivered partial content you can use instead of discarding it
• 413 Payload Too Large — not retryable until you reduce input size

Retrying a 400 or 401 wastes a request slot and won't ever succeed, since the server rejected the request itself, not the connection. Always branch on status code before deciding whether to retry.

Exponential backoff with jitter

A fixed retry delay causes "thundering herd" behavior — if ten of your requests fail at once, they'll all retry at the same instant and fail again. Exponential backoff with random jitter spreads retries out:

async function callWithRetry(fn, { maxAttempts = 5 } = {}) {
  let attempt = 0;
  while (true) {
    try {
      return await fn();
    } catch (err) {
      attempt++;
      const status = err.status;
      const retryable = [429, 500, 502, 503, 504].includes(status) || err.code === 'ECONNRESET';

      if (!retryable || attempt >= maxAttempts) {
        throw err;
      }

      const base = Math.min(1000 * 2 ** attempt, 30000);
      const jitter = Math.random() * base * 0.5;
      const delay = base + jitter;

      // Respect Retry-After header if present
      const retryAfter = err.headers?.['retry-after'];
      const wait = retryAfter ? Number(retryAfter) * 1000 : delay;

      await new Promise((r) => setTimeout(r, wait));
    }
  }
}

Key details:

• Cap the max delay so you're not waiting minutes between attempts
• Honor Retry-After when the API provides it — this is almost always more accurate than your own backoff schedule for rate limit errors
• Cap total attempts, typically 3–5. Beyond that you're likely dealing with a sustained outage or a misconfigured request, and retrying further just delays the failure the caller needs to see

Idempotency: don't double-bill yourself

A failed request doesn't always mean nothing happened. If your HTTP client times out waiting for a response, the request may have completed on the server side and generated a full completion you never received — and you'll be billed for it even though your code sees an error. Retrying blindly in this scenario can double your token spend on that call.

Mitigate this by:

1. Setting a sane timeout that's long enough for the expected response size, so you're not treating normal latency as a failure
2. Logging request IDs when available, so you can match a failed client-side request against what actually happened server-side if you need to investigate
3. Avoiding retries on ambiguous timeouts for non-idempotent operations when the downstream action (like sending the response to a user, or writing to a database) isn't itself safe to repeat

If you're building something with side effects per completion — like an agent that calls a tool to send an email — wrap the side effect separately from the Claude call, so a retried completion doesn't also retry the email send.

Retrying streamed requests

Streaming responses add a wrinkle: if the connection drops mid-stream, you may have already received and rendered partial content. Decide upfront whether to:

• Discard the partial output and retry the full request, or
• Keep the partial output and retry only for the remainder (harder to implement correctly, since the model has no memory of what it already streamed to a dropped connection)

For most use cases, discarding and retrying the full request is simpler and more reliable. If partial outputs matter to your UX, buffer them and show a "regenerating..." state rather than trying to splice a continuation.

Where SubToAPI fits

If you're already handling retries in your application code, you still need an endpoint that returns consistent status codes and headers to retry against. SubToAPI turns your existing Claude access into a standard HTTPS API with sub_live_... keys, so your retry logic — the backoff function above, your idempotency checks, your timeout handling — works against a predictable REST interface instead of something you have to reverse-engineer per provider. It also surfaces usage metadata per request, which helps when you're debugging whether a failed call actually consumed tokens before erroring out.

Setup takes a few minutes: generate a key in the dashboard, swap your base URL, and your existing retry wrapper keeps working. See the quickstart and the messages endpoint docs for request/response shapes, or the streaming guide if your retries need to account for SSE connections. Plans start at €9/month with a free trial — check pricing for details.

Questions

Should I retry on every non-2xx response? No. Only retry on 429 and 5xx errors plus network-level failures. 4xx errors other than 429 indicate a problem with the request itself that retrying won't fix.

How many retry attempts is reasonable? 3–5 attempts with exponential backoff is standard. Beyond that, surface the failure to your application logic or user rather than continuing to retry silently.

Does retrying cost extra tokens if the original request already succeeded server-side? It can, if a timeout happened after the model finished generating but before you received the response. Set realistic timeouts and log request IDs so you can investigate ambiguous failures before assuming a retry is free.