Claude Sonnet 4.5 retires on 30 November, and some of your apps may not have heard
By Brett Gavaghan, Founder of Adaptd ·
Anthropic will switch off Claude Sonnet 4.5 on the Claude API on 30 November 2026. If an app, chatbot or automation still calls it, that's the day it stops answering.
The short version
- Anthropic will retire Claude Sonnet 4.5 on the Claude API on 30 November 2026, and requests to it will then fail.
- It affects apps and automations calling claude-sonnet-4-5-20250929 on Anthropic's platforms, while Amazon Bedrock and Google Cloud set their own dates.
- Find anything still using it, switch to Claude Sonnet 5.5 and test your usual tasks before November.
AI models don't retire to the coast. They just stop answering, and whatever relied on them stops too. Anthropic has given Claude Sonnet 4.5 its date: 30 November.
What is happening to Claude Sonnet 4.5?
Anthropic is retiring Claude Sonnet 4.5 on the Claude API on 30 November 2026, after deprecating it on 30 September. Once a model is retired, requests to it fail, so anything still pointing at it stops working that day.
The recommended replacement is Claude Sonnet 5.5, released on 28 September. Anthropic's notes warn that code written for older Sonnet models can break on Sonnet 5.5 in a few ways, and point developers to a migration guide. So it's a swap, but not quite a find-and-replace.
Who does it affect?
The retirement affects businesses with apps, scripts or automations that call claude-sonnet-4-5-20250929 through the Claude API, Claude Platform on AWS or Microsoft Foundry. Amazon Bedrock and Google Cloud set their own retirement schedules, so check those separately.
Anthropic emails customers with active deployments and gives at least 60 days' notice. That email goes to whoever owns the account, which isn't always someone who still works with you. The Usage page in Claude Console can export usage by API key and model, the quickest way to see what's still calling Sonnet 4.5.
What should your business do about it?
Your business should list every tool that calls Claude with an API key and check which model each one names before November. Think of the chatbot on your website, an internal assistant, or a Zapier or Make step with an AI action that someone set up a year ago.
My advice: don't leave it to the last week of November, when everyone's also chasing invoices and planning the Christmas party. Switch to Sonnet 5.5 now, run your usual tasks through it and compare the results. Then add a quarterly reminder to check model dates. Models have a use-by date now, like the milk. Better to read the label than find out by taste.
Wondering what this means for your business?
That's exactly what the discovery call is for.