o3 left ChatGPT on Tuesday, closing the ninety-day countdown OpenAI opened back in May. On web and mobile the model simply dropped out of the picker; paid users who leaned on it are routed to the GPT-5.5 line instead. o3-pro, the higher-compute variant, survives for Pro, Team, Enterprise, and Edu seats. If you only touch o3 through ChatGPT, this is a swap you've probably already been nudged into. The part worth a calendar note is the API: those endpoints keep serving o3 until December 11, so programmatic integrations have about four months to migrate before the model disappears there too. The reasoning is the usual one — retire the lightly-used older models, point the compute at the new flagship.