On November 13, 2025, OpenAI made a significant announcement regarding the upgrade of the foundational model powering ChatGPT, transitioning from GPT-5 to GPT-5.1. This upgrade introduces two distinct versions: the Instant and the Thinking variants. The Instant version is characterized by its heightened enthusiasm and intelligence, excelling in following user instructions. It incorporates an adaptive reasoning mechanism that facilitates deeper analysis when confronted with complex issues. In contrast, the Thinking version is designed for greater clarity and ease of understanding. It processes straightforward tasks with increased speed, exhibits remarkable perseverance in tackling intricate problems, and delivers answers in a more straightforward manner, minimizing the use of technical terminology. Starting today, these new models are being progressively made available to paid subscribers, with plans to extend access to free users in the near future.