Anthropic retires Claude Sonnet 4.5 ( claude-sonnet-4-5-20250929 ) on 30 November 2026 . After that, requests to that model ID on Anthropic's API fail. Anthropic recommends Claude Sonnet 5.5 as the replacement ( Anthropic's notice ).

The ID rarely sits in one place. Check:

application code and SDK calls

.env.example and other environment defaults

Terraform variables and Helm values

notebooks and eval scripts

fallback paths that only run when something else fails

The free way

rg -n "claude-sonnet-4-5" --hidden -g '!node_modules'

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It misses IDs built from parts ( f"claude-sonnet-{ver}" ) and aliases, so read the hits around your config loaders too.

On Bedrock or Google Cloud?

Those platforms set their own retirement dates, which can differ from Anthropic's.…