AI API retirements: Claude Sonnet 4.5 retires on 30 November 2026; three OpenAI models leave the API on 1 April 2027

AI API retirements: Claude Sonnet 4.5 retires on 30 November 2026; three OpenAI models leave the API on 1 April 2027

1 October 2026: Two AI model providers have set retirement dates for models that many business applications still call. Anthropic notified developers on 30 September 2026 that Claude Sonnet 4.5 will be retired from its API on 30 November 2026. OpenAI announced on 1 October 2026 that three models will be removed from its API on 1 April 2027, and that some text-to-speech models will be removed on 6 January 2027.

Not yet independently verified. Both sources are the providers' own documentation; no independent report of these specific notices had been found at 2026-10-05. The full list of affected text-to-speech models was not read. We will update this when it can be confirmed, and remove this note.

The dates

Anthropic. According to its deprecation page, claude-sonnet-4-5-20250929 was deprecated on 30 September 2026 and retires on 30 November 2026, with claude-sonnet-5-5 as the recommended replacement. That is two months' notice.

OpenAI. Its deprecations page lists, with six months' notice:

• gpt-5.3-codex: removed 1 April 2027, replacement gpt-6-sol
• gpt-5.1: removed 1 April 2027, replacement gpt-6-sol
• gpt-5.4-nano: removed 1 April 2027, replacement gpt-6-luna

A second notice of the same day says certain text-to-speech models will be removed on 6 January 2027, with migration to gpt-realtime-2.1-mini.

Who is affected

Any company whose products, internal tools or automations call these model identifiers directly, including customer-support bots, coding tools, document processing and voice applications. Software vendors who embed these models in their own products must migrate before their customers notice.

What to do

1. Search code, configuration and prompt-management tools for the exact model identifiers above.
2. Test the replacement models on your own tasks before switching: output quality, format, latency and cost per task can all change.
3. Check pricing for the replacements and update cost forecasts.
4. Put the dates in your release plan: 30 November leaves little time for applications on Claude Sonnet 4.5.
5. Ask your SaaS vendors which models their AI features use and how they will handle these retirements.

Why it matters for buyers

Model retirements are now a routine part of buying AI. Notice periods vary from weeks to six months between providers. When choosing an AI vendor or building on one, check the published deprecation policy and how much notice it guarantees, and keep model choice configurable rather than hard-coded.

Sources

• Anthropic (Claude Developer Platform): Model deprecations - 30 September 2026
• OpenAI API documentation: Deprecations - 1 October 2026