Claude Sonnet 4 changelog

Claude Sonnet 4 and Claude Opus 4 retired

Requests to claude-sonnet-4-20250514 and claude-opus-4-20250514 on the Claude API now return an error.

Who is affected:

Apps still calling Claude Sonnet 4 or Opus 4 on the Claude API.

Action needed:

Switch to Claude Sonnet 4.6 or newer and Claude Opus 4.8 or newer.

1M context beta retired for Sonnet 4.5 and Sonnet 4

The context-1m-2025-08-07 beta header stopped working for Claude Sonnet 4.5 and Sonnet 4, so requests over 200k tokens now fail.

Who is affected:

Apps sending more than 200k tokens to Sonnet 4.5 or Sonnet 4.

Action needed:

Move long-context work to Claude Sonnet 4.6 or newer.

Claude Sonnet 4 and Claude Opus 4 deprecated

Anthropic announced that claude-sonnet-4-20250514 and claude-opus-4-20250514 would retire on the Claude API on June 15, 2026.

Who is affected:

Apps calling claude-sonnet-4-20250514 or claude-opus-4-20250514.

Action needed:

Migrate to Claude Sonnet 4.6 and Claude Opus 4.8.

Anthropic confirms three infrastructure bugs degraded Claude responses in August and September 2025

Anthropic published a postmortem saying three separate infrastructure bugs, the first introduced on August 5, intermittently degraded Claude's response quality until early September. A load balancing change on August 29 increased affected traffic. The Hacker News thread drew 381 points and 116 comments.

Who is affected:

Users of Claude Sonnet 4, Opus 4 and 4.1, and Haiku 3.5 on the Claude API and in Claude Code between August 5 and mid-September 2025.

What to do:

No action needed. Anthropic says all three bugs are fixed.