Under the hood
New helper marks most 4xx HTTP errors as non-retryable, except 401, 408, 409, 429, and 451
What
A new helper classifies HTTP status codes in the 400-499 range as non-retryable by default, with explicit exceptions for 401, 408, 409, 429, and 451, which remain retryable.
Why
This stops Claude Code from wasting time and requests retrying client errors that won't succeed on a retry (like a bad request), while still retrying the specific 4xx cases where a retry can plausibly help, like rate limiting (429) or a request timeout (408).