Claude Sonnet 4.5 is retired on November 30, 2026: calls to it will fail

What you get

A deadline. Anthropic deprecated Claude Sonnet 4.5 (claude-sonnet-4-5-20250929) on September 30, 2026 and will retire it on November 30, 2026. Their page is plain about what that means: requests to models past the retirement date will fail. The recommended replacement is claude-sonnet-5-5.

Prerequisites

An Anthropic API key in ANTHROPIC_API_KEY
Access to the code or settings where your app names its model

Steps

Find out whether you still use it. In the Claude Console, open the Usage page, click Export, and look through the file for claude-sonnet-4-5-20250929. It is broken down by API key and model.
Search your code and settings for claude-sonnet-4-5 and replace it with claude-sonnet-5-5.
Read Anthropic's migration guide before you switch: newer models changed some request settings, so a straight swap can need small edits.
Test your app with the new model well before November 30.

Test it

Run your app's normal requests with claude-sonnet-5-5 and check the replies. Then export Usage again a day later and confirm nothing is still calling the old model.

Not confirmed

These dates are for Anthropic's own API. Amazon Bedrock and Google Cloud set their own retirement dates for the same model, so check theirs if you use Claude through them.

What you'll need

What you get

Prerequisites

Steps

Test it

Not confirmed