GPT-5.1

Released November 12, 2025, GPT-5.1 was OpenAI's mid-cycle upgrade to the flagship GPT-5 series, responding directly to complaints that GPT-5 felt cold and mechanical. It splits into two variants: GPT-5.1 Instant, the default ChatGPT model optimized for warm, conversational exchanges; and GPT-5.1 Thinking, which adapts its reasoning time to problem complexity — roughly twice as fast on easy tasks, twice as slow on the hardest ones.

The release added personality presets (Professional, Candid, Quirky, Nerdy) and finer tone controls, alongside measurably better instruction following. Rolled out to Plus, Pro, Go, and Business users first, then to free users. Like the rest of the GPT-5 line it is closed weights, and its original snapshots are scheduled for API retirement on April 1, 2027.