the diff / October 7, 2026 / Claude API

Claude Sonnet 4.5 retires from the Claude API November 30

score days of notice: 61

Anthropic deprecated claude-sonnet-4-5-20250929 on September 30, 2026. Requests to it fail after November 30. The replacement is claude-sonnet-5-5.

official source: platform.claude.com →

What changed

On September 30 Anthropic deprecated Claude Sonnet 4.5, model id claude-sonnet-4-5-20250929, and set its retirement on the Claude API for November 30, 2026. Deprecated means it still answers but is no longer recommended. Retired means requests to it fail. The recommended replacement is claude-sonnet-5-5. The dates apply to the Claude API, the Claude Platform on AWS and Microsoft Foundry. Amazon Bedrock and Google Cloud set their own schedules.

Why it matters if you ship with an agent

Grep your repos for the id. An agent config, subagent definition or CI script written last autumn has a fair chance of pinning it, and the agent that pinned it will not warn you when it stops. The Usage page in the Claude Console exports a CSV of calls by API key and model, which finds the ones your repo does not. Swap to claude-sonnet-5-5 and rerun whatever tests cover the output. That is 54 days from today.

Source: https://platform.claude.com/docs/en/about-claude/model-deprecations

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