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openai/gpt-5-3-codex
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GPT-5.3-Codex

GPT-5.3-Codex is OpenAI’s most advanced agentic coding model, combining the frontier software engineering performance of GPT-5.2-Codex with the broader reasoning and professional knowledge capabilities of GPT-5.2. It achieves state-of-the-art results on SWE-Bench Pro and strong performance on Terminal-Bench 2.0 and OSWorld-Verified, reflecting improved multi-language coding, terminal proficiency, and real-world computer-use skills. The model is optimized for long-running, tool-using workflows and supports interactive steering during execution, making it suitable for complex development tasks, debugging, deployment, and iterative product work. Beyond coding, GPT-5.3-Codex performs strongly on structured knowledge-work benchmarks such as GDPval, supporting tasks like document drafting, spreadsheet analysis, slide creation, and operational research across domains. It is trained with enhanced cybersecurity awareness, including vulnerability identification capabilities, and deployed with additional safeguards for high-risk use cases. Compared to prior Codex models, it is more token-efficient and approximately 25% faster, targeting professional end-to-end workflows that span reasoning, execution, and computer interaction.

2/24/2026
400,000 tokens

Specifications

Modalities

Input
text
image
file
Output
text

Supported Parameters

include_reasoning
max_tokens
reasoning
response_format
seed
structured_outputs
tool_choice
tools

Max Output Tokens

128,000

Reasoning Configuration

Default
Thinking on (effort: medium)
Selectable effort levels
xhigh
high
medium
low
none
Turning thinking off
Possible (reasoning.enabled: false)

How to control thinking, and what it costs

Frequently asked questions

Is GPT-5.3-Codex available on FastMetal?
Not at the moment. GPT-5.6 Sol, from the same lab, is available on the FastMetal API today.
What is the context window of GPT-5.3-Codex?
400,000 tokens, shared between the prompt and the response.