Model components / Fine-tuned / chat models

o3 / o4-mini

Previous reasoning tier (2025): full-scale o3 plus cost-efficient o4-mini, both using extended chain-of-thought. Powered Codex agent and ChatGPT's coding mode through 2025. Folded into the GPT-5 line in late 2025; OpenAI consolidated the o-series and GPT branches and is no longer maintaining o-series as a separately branded reasoning family. Current reasoning capability lives in GPT-5.x with thinking enabled and in GPT-5.3-Codex.

OpenAI o3 and o4-mini reasoning models, both released Apr 16 2025 (o3-mini preceded Jan 31 2025). Post-trained reasoning/instruct models, API-only + ChatGPT, no downloadable weights. Verified via OpenAI system card + Wikipedia June 2026; succeeded by GPT-5.x reasoning line but still selectable/available.

Openness

1 high confidence

1.0

weights: closed
data: closed
code: closed
license: Proprietary(API+ChatGPT only)

Proprietary OpenAI reasoning models; no weights, data, or code released.

https://en.wikipedia.org/wiki/OpenAI_o3 recorded 2026-06-04
o3/o4-mini are proprietary reasoning models served via ChatGPT/API, released Apr 16 2025
https://cdn.openai.com/pdf/2221c875-02dc-4789-800b-e7758f3722c1/o3-and-o4-mini-system-card.pdf recorded 2026-06-04
OpenAI o3 and o4-mini System Card, Apr 16 2025 (primary)

Adoption

5 medium confidence

5.0

o3/o4-mini were rolled out as selectable models inside ChatGPT (Plus/Pro and some free) plus the API; ChatGPT reached ~900M WAU (Feb 2026) rising toward ~1B (May 2026). Reach attributed to the ChatGPT surface these models power, not a standalone o3 count. Now superseded as default by GPT-5.x but still used at scale.

https://en.wikipedia.org/wiki/OpenAI_o3 recorded 2026-06-04
o3/o4-mini available to ChatGPT users and API

Capability

4 high confidence

4.0

Frontier-class reasoning at Apr 2025 launch (SOTA on Codeforces/SWE-bench/MMMU at the time). By June 2026 surpassed by GPT-5.x / Opus 4.8 (88.6 SWE-bench) / Gemini 3.5, so frontier-relative score is 4, not 5.

https://en.wikipedia.org/wiki/OpenAI_o3 recorded 2026-06-04
o3 SWE-bench Verified 71.7, GPQA 87.7, Codeforces 2727; o4-mini AIME/GPQA figures
https://cdn.openai.com/pdf/2221c875-02dc-4789-800b-e7758f3722c1/o3-and-o4-mini-system-card.pdf recorded 2026-06-04
primary system-card benchmark evaluations

Unchanged since 2026-07-29 (last edited, not re-checked)