Farhan Arshad

Sonnet 4.5 retires 30 November

Run your own request on Claude Sonnet 4.5 and Sonnet 5.5, see what breaks, and see what the same job costs on each. Free, from farhanarshad.com.

1. Your API key

Use a throwaway key made for this test, and delete it when you are done.

2. A real prompt from your work

Results

Sonnet 4.5 (claude-sonnet-4-5-20250929)

Not run yet.

Sonnet 5.5 (claude-sonnet-5-5)

Not run yet.
Run a test to see the result here.

Prices used: Sonnet 4.5 $3 input and $15 output per million tokens; Sonnet 5.5 $2 input and $10 output per million tokens (Claude pricing page, read 6 Oct 2026). Sonnet 5.5 counts the same text as roughly 30% more tokens and thinks by default, so only your own run tells you the real difference.

3. Where the old name hides

Search every one of these for sonnet-4-5 and sonnet-4.5. (Sonnet 4.6 is not on this notice.)

  • Your code and settings: .env files, settings files, shared helper functions, default values.
  • Automation tools: Make modules, n8n nodes, Zapier steps, anything with a model dropdown that was set once and forgotten.
  • Routers and gateways: OpenRouter presets, LiteLLM or similar configs.
  • Cloud consoles: if you reach Claude through Amazon Bedrock or Google Vertex, check their own model pages for their dates too.
  • Your Claude Console usage page: check if you can group it by model, and see what still calls Sonnet 4.5.

Anthropic's notice is for the Claude API: claude-sonnet-4-5-20250929 retires on 30 November 2026, replacement claude-sonnet-5-5 (Anthropic model deprecations page, read 6 Oct 2026).