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Model · OpenAI · Code

GPT-5.3-Codex

OpenAI's most capable agentic coding model — tuned for long-horizon software engineering, tool use, and the Codex agent surface.

Modality
Code
License
Proprietary (Proprietary)
Context window
400,000 tokens
Released
February 5, 2026
Last verified
June 8, 2026
Runs locally
No
Also handles
text

Strengths

  • Most capable OpenAI model for agentic, multi-step coding
  • 400k-token context (128k max output)
  • Powers the Codex agent in ChatGPT and the API

Weaknesses

  • Specialised for coding/agentic work rather than general chat
  • Closed weights — API/product only

Try it

WhereTypeNotes
OpenAI API hosted-api API key required
ChatGPT / Codex product Codex agent surface

Version history

  1. GPT-5.5 Apr 2026
  2. GPT-5.4 mini Mar 2026
  3. GPT-5.3-Codex Feb 2026 Current

Official sources

Change log

  • — Initial entry (2026-06-08 catalog refresh, Tier 3). Released 2026-02-05; OpenAI's flagship agentic coding model.

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