GPT-5, released August 7, 2025, collapsed OpenAI's confusing two-track lineup — GPT-4.1 for speed, o3 for reasoning — into a single system with a router that decides per request how much thinking a question deserves. It launched simultaneously in mini, nano, and Pro variants and became the default for ChatGPT's hundreds of millions of users, including the free tier.

The launch drew a famously mixed reception: benchmark gains over o3 were real but incremental, and the router initially frustrated users who wanted explicit model control. OpenAI iterated quickly — GPT-5.1 in November 2025 reworked the model's personality and adaptive reasoning, and the GPT-5.x line has carried OpenAI's flagship branding ever since.