Anthropic sets Nov. 30 retirement date for Claude Sonnet 4.5 AI model
Software that still calls the model after that date will get errors, and Anthropic points developers to Claude Sonnet 5.5.
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Anthropic told developers on September 30, 2026 that Claude Sonnet 4.5, one of its AI models, will be retired on November 30, 2026 [1]. The company’s deprecation page lists claude-sonnet-5-5, or Claude Sonnet 5.5, as the recommended replacement for the Sonnet 4.5 model ID, claude-sonnet-4-5-20250929 [1].
Retirement means the model stops working. Anthropic’s documentation says requests to a retired model fail, so software still calling Sonnet 4.5 after November 30 would return errors instead of answers [1]. The page says Anthropic gives at least 60 days’ notice before retiring a publicly released model, and that it notifies affected customers by email and in the documentation [1].
The dates apply to the Claude API, which is the connection that software uses to send requests to Claude, and to Claude Platform on AWS and Microsoft Foundry [1]. Amazon Bedrock and Google Cloud are run by partners and set their own retirement schedules, so dates there can differ [1].
The same page lists Claude Sonnet 5.5 as active, with a tentative retirement date of not sooner than September 28, 2027 [1].
Most small businesses do not call an AI model directly. They use one inside a product from a software company, such as a website chatbot, a phone answering assistant or a tool that drafts replies to customers. If a vendor built that product on Sonnet 4.5, the switch to a newer model is the vendor’s to make before November 30 if the tool is to keep working.
Anthropic’s notice goes to developers, so a business owner hears about it only if the vendor mentions it. A swap can also change how replies read, which is why Anthropic’s page recommends testing replacement models well before the retirement date [1]. An owner can ask a vendor which AI model sits behind a tool and whether it is moving off Sonnet 4.5.
- November 30, 2026: scheduled retirement of Claude Sonnet 4.5 on Anthropic’s own platforms [1].
- Amazon Bedrock and Google Cloud publish their own schedules for the same model, so vendors that run Claude through those services may have a different date [1].
- The page also lists Claude Haiku 4.5 with a tentative retirement date of not sooner than October 15, 2026, and Claude Opus 4.5 not sooner than November 24, 2026. Neither is marked deprecated [1].