Quick answer
GPT-4o (pronounced "four-oh") is OpenAI's multimodal model — it handles text, images, audio, and video in one unified model. The "o" stands for "omni," meaning all types of input. It is faster and cheaper than GPT-4, and it powers the free tier of ChatGPT. GPT-5 has now replaced it as OpenAI's most capable model.
When OpenAI released GPT-4o in May 2024, it was a significant step. Not because it was smarter than GPT-4, but because it changed how AI models handle different types of information. Here is what actually changed.
What does "omni" actually mean?
Previous models handled different input types separately. GPT-4 could understand text. With plugins, it could also analyse images — but that was a different pipeline bolted on. GPT-4o processes text, images, audio, and video natively in a single model. It sees, hears, and reads without switching between different systems.
What GPT-4o can do that GPT-4 could not
- Real-time voice conversation — responds in 320ms on average (similar to human response time)
- Emotional tone detection in voice — can tell if you sound frustrated or happy
- Live image analysis — you can point your camera at something and ask about it
- Reads and describes charts, diagrams, and handwritten notes natively
- Switches between languages mid-conversation more smoothly
GPT-4o vs GPT-4 — the practical difference
On text-only tasks, the quality difference between GPT-4 and GPT-4o is small. GPT-4o is faster and cheaper, which is why OpenAI made it the default. The real difference shows on multimodal tasks — anything involving images, voice, or a combination of input types.
GPT-4o mini is a smaller, faster, cheaper version of GPT-4o. It powers the free tier of ChatGPT for many tasks. It is less capable than full GPT-4o but remarkably good given its cost — roughly 15x cheaper per token than GPT-4.
Where does GPT-4o fit now that GPT-5 exists?
GPT-5 is more capable than GPT-4o on reasoning and complex tasks. But GPT-4o remains relevant because it is cheaper and faster. Many developers use GPT-4o (or GPT-4o mini) for the 80% of tasks where it is "good enough" — and reserve GPT-5 for the complex 20%.
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Bottom line
GPT-4o was the model that made AI feel genuinely conversational — you could talk to it, show it things, and it responded naturally. GPT-5 has since pushed capability further, but GPT-4o remains the workhorse of the OpenAI product line because of its speed and cost.