Issues with responses using structured outputs on the API

What to do

• Check whether your product depends on Anthropic. Check your stack

  Paste a package.json, lockfile, Terraform or a list of domains at down.guide/stack to see every provider you depend on.

• Confirm your retries, queues and scheduled jobs caught up after the 0m it lasted.

  Anything that failed between 2026-04-23 21:25 UTC and 2026-04-23 02:00 UTC may need a replay.

• Subscribe to Anthropic's feed to hear about the next one first. RSS feed

  https://down.guide/feed?provider=anthropic works in Slack (/feed subscribe), Discord feed bots and any RSS reader.

Updates from Anthropic 1

1. resolvedApr 23, 2026, 2:00 AM UTC

   We have identified and resolved an issue which resulted in issues with model responses when making use of structured outputs via the Anthropic API between 16:10 UTC on April 22 and 01:59 UTC on April 23. During this period, structured outputs containing some forms of grammar requirements returned with reduced quality. This did not impact any requests not using structured outputs, as detailed here: https://platform.claude.com/docs/en/build-with-claude/structured-outputs.

   provider

Corrections

None so far.

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