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GPT-5.3-Codex

GPT-5.3-Codex is OpenAI’s agentic coding model for repository-scale software engineering and long-running code tasks, with a 400K context and $1.75/M input pricing.

Coding ModelsTextImage Paid
In plain English

What is this model and why does it matter?

GPT-5.3-Codex is OpenAI's agentic coding model for repository-scale software engineering and long-running code tasks.

Agentic codingRepository workBug fixingCodebase migrationSoftware engineering agents
Model overview

GPT-5.3-Codex: features, use cases and important details

GPT-5.3-Codex is a current AI model verified from first-party OpenAI sources.

GPT-5.3-Codex verified specifications

GPT-5.3-Codex is OpenAI’s agentic coding model for repository-scale software engineering and long-running code tasks. Its verified context or usage limit is 400000 tokens, with 128000 tokens maximum output.

GPT-5.3-Codex pricing and access

GPT-5.3-Codex costs $1.75 per 1M input tokens, $0.175 per 1M cached input tokens and $14 per 1M output tokens.

GPT-5.3-Codex best uses

Agentic coding, Repository work, Bug fixing, Codebase migration, Software engineering agents.

GPT-5.3-Codex limitations

Generated code must be tested, No fine-tuning, Can still make repository-level mistakes.

Get started

How to use this model

  1. Create an OpenAI API key.
  2. Call gpt-5.3-codex.
  3. Choose reasoning effort.
  4. Provide repository context and optional images.
  5. Use function tools or structured outputs for agent workflows.
Copy and try

Example prompts

  • Fix the failing tests in this repository.
  • Implement this feature across the relevant files.
  • Review this architecture and create a migration patch plan.
Capabilities

What it can do

  • 400K context
  • 128K output
  • Agentic coding
  • Image input
  • Function calling
  • Structured outputs
  • Reasoning controls
Best for

Practical use cases

  • Coding agents
  • Large repositories
  • Refactoring
  • Debugging
  • Software migration
Pricing

What does it cost?

GPT-5.3-Codex costs $1.75 per 1M input tokens, $0.175 per 1M cached input tokens and $14 per 1M output tokens.

Input$1.75 / 1M tokens
Output$14 / 1M tokens
Simple summaryCoding-focused pricing is $1.75/M input and $14/M output.

What stands out

  • Specialized for agentic coding
  • Large context
  • Competitive input price

Things to consider

  • Coding-specialized rather than general flagship
  • Proprietary
Limitations

Important restrictions and trade-offs

  • Generated code must be tested
  • No fine-tuning
  • Can still make repository-level mistakes
SimplifyAITools verdict

Our editorial take

A strong SEO target for developers comparing current Codex models and autonomous software-engineering agents.

References

Primary sources

  1. Open source 1 ↗
  2. Open source 2 ↗
  3. Open source 3 ↗
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