OpenAI introduced GPT-4o — 'o' for omni — a single model natively handling text, vision, and audio with response times approaching human conversation. It was faster and cheaper than GPT-4 Turbo, and unusually, it rolled out to free ChatGPT users too, with usage limits.

The headline feature was Advanced Voice Mode, letting users talk to ChatGPT nearly in real time with interruptions and emotional tone. It began rolling out to Plus users in late July and became one of the product's signature experiences.

GPT-4o remained the flagship for over a year and developed an unusually loyal following — its eventual removal from ChatGPT years later prompted genuine user backlash over its personality.