A long-announced OpenAI API shutdown lands today, October 23: o1, o1-pro, o3-mini, o4-mini, GPT-4, GPT-4 Turbo, GPT-3.5 Turbo, GPT-4.1 nano, the May 2024 GPT-4o snapshot and GPT-Image-1 all stop working in the API, along with fine-tuned versions built on several of them. OpenAI set the date in a deprecation notice dated April 22, and each model has a named substitute, mostly from the GPT-5.6 family — Sol for most, Terra for GPT-3.5 Turbo and o4-mini, and Luna for 4.1 nano.

The practical risk is not the apps people watch every day, which get fixed fast when they break. It is the quiet jobs nobody owns: overnight scripts, agent steps and no-code tools still pinned to an old model ID, which will now fail silently until someone notices the backlog.

Developers who have not yet migrated should search their code, environment variables and tool settings for the retired IDs, swap in the listed substitute, and run a real input through it, since a newer model can answer in a different shape than the one it replaces. This is one wave in a longer shutdown calendar that already retired older snapshots in July and September.