Anthropic 429 with no retry-after header: that is the monthly spend cap, and retries will never work

429 with no retry-after: stop retrying, check billing

Symptom

Every request returns HTTP 429, rate_limit_error. The response has no retry-after header, and waiting plus retrying changes nothing.

Confirm the cause

Look at error.details.error_code on the Messages API response. If it is enforced_spend_limit_reached, your organization hit its tier's monthly spend cap, not a rate limit. Spend-cap pauses last until 00:00 UTC on the first day of the next month. Note a related but different case: a 400 with the message starting "You have reached your specified API usage limits" is a spend limit you set yourself on the billing page, not the tier cap.

Fix

1. Confirm on the Billing page in the Claude Console what the cap and current spend are.
2. To restore access now, request a higher limit (Rate limits page) or contact support for urgent needs.
3. If the 400 variant, raise or remove the self-set limit on the billing page.
4. Do not burn retry budget on this: the SDK's automatic retries fail until access resumes.

Verify

After the limit is raised, requests succeed immediately with the same payload. Log which error_code you saw so the next on-call does not treat it as a rate limit.

The rate limits doc distinguishes the tier spend-cap 429 (no retry-after, errorcode enforcedspendlimitreached) from ordinary rate limits, and documents the self-set spend limit 400. Verified live at https://docs.anthropic.com/en/api/rate-limits and https://docs.anthropic.com/en/api/errors.