OpenAI shipped GPT-5.1 as a ChatGPT update with two modes — GPT-5.1 Instant and GPT-5.1 Thinking — and, more unusually, let users select alternative assistant personalities including 'friendly,' 'efficient,' and 'cynical.'

The release also improved coding steerability and reduced the 'overthinking' problem where reasoning models wasted compute on simple questions.

A coding variant, GPT-5.1-Codex-Max, followed on November 18, foreshadowing OpenAI's return to specialized coding models.