November 12, 2025 — OpenAI released GPT-5.1, splitting the model into an Instant mode for everyday requests and a Thinking mode for harder, multi-step problems.
What happened
OpenAI rolled out GPT-5.1 across ChatGPT and its API roughly three months after GPT-5, packaging the update as two selectable modes: GPT-5.1 Instant for fast, conversational answers and GPT-5.1 Thinking for tasks that benefit from extended reasoning. OpenAI said the update improved response style, instruction-following and reasoning quality relative to GPT-5.
Why it matters
The Instant/Thinking split makes the reasoning-versus-speed trade-off an explicit, user-facing choice rather than something hidden inside routing logic, which affects how teams design prompts, set cost budgets and test latency-sensitive applications.
Security and infrastructure impact
Any organization that had just finished evaluating GPT-5 for production use needed to re-test against GPT-5.1’s two modes, reinforcing why security and IT teams increasingly treat frontier-model upgrades as scheduled change events with their own review cycle rather than one-time approvals.
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