Checklists for the deadlines in front of you
Each note covers one shutdown or one recurring problem: what changes, what breaks, and the steps in order.
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Claude Sonnet 4.5 retires on November 30, and API version 2026-10-21 rejects temperature: a regression plan
Anthropic retires claude-sonnet-4-5-20250929 on November 30, 2026. The new API version and SDK majors reject temperature, top_p and top_k. How to migrate to claude-sonnet-5-5 without a regression.
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Custom GPTs retire on December 11: actions and sharing don't transfer. A migration checklist
OpenAI retires ChatGPT custom GPTs on December 11, 2026. Instructions and files migrate to plugins, but custom actions, the selected model and sharing settings do not. What to check, in order.
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GPT-4o and GPT-4.1 shut down on January 14, 2027: what breaks when you move to a reasoning model
OpenAI shuts down gpt-4o, gpt-4o-mini, gpt-4.1, gpt-4.1-mini and their fine-tunes on January 14, 2027. The replacement, gpt-6-luna, is a reasoning model, so tool calls and parameters change. A migration checklist.
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