GPT-5.3 Codex

OpenAI · February 2026

Built for programming: writing, reviewing and fixing code, and working through long tasks on its own. Not meant for general chat.

Best for: Coding, deep reasoning, and agent workflows

Context window
400,000 tokens
≈ 300,000 words · about 1,200 pages
Max output
128,000 tokens
≈ 96,000 words in a single answer
Knowledge cutoff
August 2025
its training cutoff

Modalities

TextInput and output
ImageInput only
AudioNot supported
VideoNot supported

Reasoning effort

None
Low
Medium
High
X-High

Features

StreamingSupported
Function callingSupported
Structured outputsSupported
Fine-tuningNot supported

Tools

Web searchSupported

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