API error fixes & troubleshooting

Short, accurate fixes for the errors that actually stop developers mid-build on the Claude and OpenAI APIs — what each error means, how to tell look-alike errors apart, and the retry/backoff patterns that resolve them. Every page is verified against the provider's current documentation.

Claude API errors

• Claude API overloaded_error (HTTP 529) — why it happens, how it differs from a 429, and the backoff pattern to handle it.
• Anthropic API 401 authentication_error — the 6 root causes of a bad API key, 401 vs 403, the .strip() whitespace fix, and how to check key prefix (sk-ant- vs sk-proj-).

OpenAI API errors

• OpenAI API 429: rate limit vs. quota — the same status code, two opposite causes (rate_limit_exceeded vs insufficient_quota), and how to fix each.
• OpenAI context_length_exceeded (400) — how to count tokens with tiktoken, the context window table for all current models, and the 5 fix strategies ranked by trade-off.
• OpenAI model_not_found (404) — wrong model ID, no access, or deprecated model: 3 causes with a current valid-ID reference and a deprecation migration table.
• OpenAI API timeout errors — connect vs. read timeout types, SDK defaults, configuring httpx.Timeout, and the retry-safety decision tree for long-running requests.

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