Model · OpenAI · Reasoning
o3
OpenAI's flagship reasoning model. Uses extended chain-of-thought before answering, trading latency for depth on math, science, and complex coding tasks.
- Modality
- Reasoning
- License
- Proprietary (Proprietary)
- Context window
- 200,000 tokens
- Released
- April 16, 2025
- Last verified
- July 10, 2026
- Runs locally
- No
Strengths
- Top-tier on math, scientific reasoning, and competition-level coding
- Strong tool use during reasoning chains
Weaknesses
- High latency — not suitable for chat-paced UX
- Closed weights
- Reasoning tokens are billed and can dominate cost
Try it
| Where | Type | Notes |
|---|---|---|
| OpenAI API | hosted-api | API key required |
| ChatGPT | product | Plus/Team/Enterprise |
Version history
- o3 Apr 2025 Current Deprecated
- o4-mini Apr 2025 Deprecated
Official sources
- Model docs docs
Change log
- — Deprecated — superseded by GPT-5.5. OpenAI's deprecations page now lists an API shutdown of 2026-12-11 for o3-2025-04-16 (announced 2026-06-11), reversing the prior 'no API change' position recorded below.
- — Verified current. o3 remains available in the API — OpenAI is retiring it from ChatGPT only (2026-08-26), with no API change. GPT-5.5 is the newer reasoning-capable flagship.
- — Initial entry.
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