According to OpenAI's model release notes, GPT-4.5 will be retired from ChatGPT on June 27, 2026, following a 30-day sunset period, while o3 will be removed on August 26, 2026, after a 90-day window.
GPT-4.5 was OpenAI's largest and most expensive model before GPT-5 arrived. o3 was positioned as a reasoning-first alternative to GPT-4o before the company introduced newer reasoning models. The retirements confirm that OpenAI is cycling through model generations at a faster pace than at any point in the company's history.
Developers using these models via the API have been advised to migrate before the retirement dates. Specific API deprecation timelines for the developer tier were not announced in the same notice.