Anthropic API · api · fg-0577

Requests to claude-sonnet-4-5-20250929 will fail after the November 30, 2026 retirement

If you see Requests pinned to claude-sonnet-4-5-20250929 start returning errors after November 30, 2026, the cause and the fix for Anthropic API are below, last verified 2026-10-30.

Verified Oct 2026trust 50/100

Symptom

Requests pinned to claude-sonnet-4-5-20250929 start returning errors after November 30, 2026Model not found style errors in production with no code change

Cause

Claude Sonnet 4.5 was deprecated on September 30, 2026, and retirement on the Claude API is scheduled for November 30, 2026. Pinned model IDs stop working on that date.

Fix

Move to claude-sonnet-5-5 before the date. Sonnet 5.5 has its own breaking changes: use thinking type between_tools instead of disabled, drop tool_choice any and tool, and use the newer computer use toolset. Test before switching.

Apply

model="claude-sonnet-5-5" # replaces claude-sonnet-4-5-20250929

Affected

Claude API, claude-sonnet-4-5-20250929, retirement scheduled 2026-11-30

Sources

https://platform.claude.com/docs/en/release-notes/overview

Last verified 2026-10-30 · Confirmed by 0 builders

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Have your agent know this before it fails

$ /plugin marketplace add getfootgun/footgun

$ /plugin install footgun@footgun