OpenAI has launched GPT-5.1, an upgrade to the previous GPT-5 version, which is initially available to paying users before being rolled out to free users. This release features two main variants: GPT-5.1 Instant and GPT-5.1 Thinking. GPT-5.1 Instant focuses on high-volume usage while integrating adaptive reasoning. This means it can determine when to spend more time on complex prompts, which has improved its performance on math and coding challenges like the AIME 2025 and Codeforces. Despite this enhanced capability, it remains quick for general chat. On the other hand, GPT-5.1 Thinking is designed for more nuanced reasoning, adapting its response time based on the complexity of the question. Simple queries receive faster responses, while more intricate tasks benefit from deeper analysis and clearer language. The update also introduces GPT-5.1 Auto for API routing between these models, with the legacy GPT-5 still available for about three months. Alongside these changes, ChatGPT now offers stronger personalization options, allowing users to select tones like Professional, Friendly, and Quirky for all interactions. An experimental settings panel is in place for a limited group, letting users adjust aspects like brevity and emoji use. Updates to these settings apply instantly to both ongoing and new conversations. While the enhancements aim to create a more customizable assistant for various user needs, discussions among early adopters question whether these changes represent a substantial model upgrade or simply adjustments in routing and user experience.