Free ChatGPT o1, now upgraded to GPT-5

Looking for ChatGPT o1 for free? OpenAI has since replaced o1 with newer models, so the chatbot on this page now runs GPT-5. It’s free, unlimited and needs no account: type your question above and you’re good to go.

What was OpenAI o1?

OpenAI introduced o1 in September 2024 (first as “o1-preview”, then as the full o1 in December). It was OpenAI’s first “reasoning” model: instead of answering straight away, it spent time working through a problem step by step before replying. That made it much better than GPT-4o at math, science and coding, at the cost of slower answers.

What happened to o1?

OpenAI kept improving its reasoning models: o3 and o4-mini followed in April 2025. Then, in August 2025, GPT-5 brought quick answers and deeper reasoning together in a single model and became ChatGPT’s default. Since then, OpenAI has also launched the GPT-6 family. That’s why this page now uses GPT-5: offering o1 today would mean giving you an older model.

How to get well-reasoned answers

o1 was popular for hard problems. To get the most out of the chatbot on this page for that kind of question:

• Give all the data: the full problem statement, the numbers, the constraints.
• Ask it to reason step by step and to show its working.
• Ask it to check its answer, or to solve the problem a second way.
• Break long problems down: one part at a time works better than everything at once.
• Stay critical: check results that matter, especially in math and code.

Free and unlimited, for real

On Yiaho, there’s no message counter, no account and nothing to install, on a computer or a phone. Yiaho is funded by ads and isn’t affiliated with OpenAI; we use OpenAI’s official API. For OpenAI’s latest generation, try GPT-6 Luna, which is free on Yiaho too, or our free ChatGPT page.

ChatGPT o1 FAQ

Can I still use ChatGPT o1 for free?

Not on Yiaho: the chatbot on this page now runs GPT-5, OpenAI’s newer model. It’s free and unlimited.

Is GPT-5 better than o1?

GPT-5 is a newer model that combines fast answers and step-by-step reasoning in one system. For everyday questions it’s faster than o1 was, and you can ask it to reason carefully when a problem is hard.

Do I need an account?

No. Just type your question in the chat box at the top of the page.

Can I download ChatGPT o1?

There’s nothing to download here: the chatbot works in your browser. Be wary of websites offering a “ChatGPT o1 download”.