Should I retry Anthropic 400 invalid_request_error?

No. Fix the cause first: Read error.message: it names the field (for example messages.1.content.0).

AI API errors / Anthropic (Claude)

Anthropic (Claude) · HTTP 400 · checked Oct 24, 2026

Anthropic 400 invalid_request_error: what it means and how to fix it

Do not retry: fix it first

400 invalid_request_error

What it meansSomething in the request itself is wrong: a missing or misnamed field, a bad value, messages in the wrong order, or a feature the model does not support. Anthropic also returns 400 when you hit a spend limit you set yourself on the organization or a workspace.

How to fix it

Read error.message: it names the field (for example messages.1.content.0).
Check the model supports what you sent (thinking type, tool_choice, tool versions, prefill). The pages below cover the common ones.
If the message mentions a spend limit, raise the limit you set in the Console.

Handle it in code

import anthropic

# The SDK retries 429, 5xx and connection errors with exponential backoff and honors retry-after.
client = anthropic.Anthropic(max_retries=6)

try:
    msg = client.messages.create(model="claude-sonnet-5-5", max_tokens=1024,
                                 messages=[{"role": "user", "content": "Hello"}])
except anthropic.RateLimitError as e:      # 429 after all retries
    print("still rate limited", e.response.headers.get("retry-after"))
except anthropic.APIStatusError as e:      # 529 overloaded, 500, 504...
    print(e.status_code, e.response.headers.get("request-id"))

The official SDKs already retry connection errors, 429 and 5xx twice with exponential backoff and honor retry-after; raise max_retries for batch jobs.

Same kind of error at other providers

Other Anthropic (Claude) errors

Source

Anthropic (Claude) error documentation: platform.claude.com/docs/en/api/errors (checked Oct 24, 2026)

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