o3 is OpenAI's advanced reasoning model that succeeds o1, delivering stronger chain-of-thought performance on mathematical, scientific, and coding problems with improved efficiency and full tool support.
import { streamText } from 'ai'
const result = streamText({ model: 'openai/o3', prompt: 'Why is the sky blue?'})o3 was released on April 16, 2025 as the successor to o1 in OpenAI's reasoning model series. It advances the chain-of-thought paradigm introduced by o1-preview: the model generates internal reasoning tokens, working through problems step by step, checking its work, and trying alternative approaches before producing a final answer.
o3 improves on o1 across key reasoning benchmarks while using reasoning tokens more efficiently. It launches with the full set of production API features: function calling for tool use, structured outputs via JSON schema constrained decoding, vision input for reasoning over images and diagrams, and developer system messages for behavioral control.
The context window of 200K tokens accommodates the lengthy inputs that complex reasoning tasks demand. The model also supports the reasoning_effort parameter, letting you control how deeply it thinks on a per-request basis for efficient handling of mixed-difficulty workloads.