Lineage · Since 2024
The OpenAI o1 lineage
OpenAI's reasoning-first model line, which spends inference-time compute on a private chain of thought before answering.
Generation 1 · Dec 5, 2024
OpenAI o1
OpenAI o1 is a reasoning model that thinks through a problem internally before replying, trading latency and cost for much higher accuracy on maths, science and difficult programming tasks. It reached general availability in December 2024 and set the template for later reasoning models.
Closed200K ctxMultimodalExtended step-by-step reasoning before answeringCompetition-level mathematics and physics problems
Generation 2 · Apr 16, 2025
OpenAI o3
OpenAI o3 is the successor to o1 in OpenAI's reasoning line. Released in April 2025, it can call tools such as web search and Python while it reasons, and it reasons over images as well as text.
Closed200K ctxMultimodalDeeper reasoning than o1Uses tools (search, code, images) inside its reasoning