OpenAI Removes GPT-5.1, GPT-5.3-Codex and GPT-5.4-Nano from the API

GPT-5.1 and GPT-5.3-Codex (replacement gpt-6-sol) and GPT-5.4-Nano (replacement gpt-6-luna) are removed from the OpenAI API, per the Oct 1, 2026 notice.