GPT-4o — the "o" stands for omni — launched May 13, 2024 as OpenAI's first natively multimodal model, trained end-to-end across text, vision, and audio rather than stitching separate models together. Its headline feature was real-time voice conversation with near-human response latency, demoed live the day before Google I/O.

GPT-4o also marked a strategic shift: it brought GPT-4-class intelligence to ChatGPT's free tier for the first time, at half the API price of GPT-4 Turbo. The smaller GPT-4o mini followed in July 2024 and displaced GPT-3.5 as the default cheap model. GPT-4o remained ChatGPT's workhorse until the GPT-5 launch in August 2025.