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Anthropic API errorAnthropic API 529: overloaded_error

Your app’s Claude API calls fail with HTTP 529 and overloaded_error, or a streamed reply stops with an error event after starting normally. A 529 means the API is temporarily overloaded, which can happen when traffic is high across all users, so it usually isn’t a bug in your request. What you control is how your app retries, what users see meanwhile, and whether one failure loses work. Here’s how, or hand it over at a fixed price.

Short answer

Let the official SDK retry with backoff, and raise max_retries if two retries aren’t enough for your traffic. Handle error events inside streams, since those arrive after a 200 response. Show users a clear retry message or queue the job instead of failing silently. A 429 at a sudden traffic jump is a different limit: ramp traffic up gradually.

What causes it, and what you can control

  1. 01

    The API is overloaded for everyone

    “A 529 error can occur when the API experiences high traffic across all users.” Anthropic, Errors

    A 529 comes from Anthropic’s side during high traffic, so there’s nothing to fix in your request. Check the status page, keep the request ID from the response for support, and design the app to ride it out.

  2. 02

    Your app gives up too early

    “with exponential backoff, twice by default, honoring the retry-after header when present.” Anthropic, Errors

    The official SDKs retry 5xx errors with exponential backoff, twice by default. If your code catches the first error and fails, or you call the API without an SDK, a short burst of 529s becomes a user-facing error. Use the SDK’s retries, raise max_retries for background jobs, and keep user-facing calls short enough to fail fast with a clear message.

  3. 03

    Streamed replies fail after they start

    “an error can occur after the API returns a 200 response.” Anthropic, Errors

    With streaming, the response can start with 200 and then carry an error event, which your HTTP error handling never sees. Listen for error events in the stream, keep the text received so far, and offer a retry.

  4. 04

    A 429 after a sudden jump in traffic

    “increase your traffic gradually and maintain consistent usage patterns.” Anthropic, Errors

    If you see 429 rather than 529 right after a launch or a batch job starts, in rare cases you may have hit acceleration limits. Spread the load out and increase it over time.

Checked against the vendor’s docs on : Anthropic: Errors; Anthropic: Status page.

Rather hand it over?

Fixed scope, fixed price, paid upfront. The work happens in writing; no call needed.

Related: OpenAI 429 insufficient_quota · Building apps with the Claude API · AI integration services

Questions

More on this error

Should I switch to another model when I get 529s?

Only to a model you’ve already tested on the same prompts. A fallback that gives different answers can be worse than a short retry message.

How long does a 529 last?

Anthropic’s docs don’t say. Treat it as temporary, retry with backoff, and check the status page if it continues.

Can you fix it for me?

Yes, for the app side: the App Fix Ticket gives you a written diagnosis first, then the fix, and the API Integration offer adds retries, logs, failure alerts and tests. Neither can change Anthropic’s capacity or uptime.

A different error?

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