OpenAI
Chat with GPT-5.3 Codex online
OpenAI's coding agent — debugging, reviewing, deploying, not just writing the function.
400K tokens
Context
128,000 tokens
Max output
Balanced
Speed
What you’ll use it for
Agentic development
Whole tasks across the lifecycle, not one snippet.
Debugging
Reads real failures and works towards the cause.
Code review
Reviews a change against the intent behind it.
Screenshot to fix
Takes images, so a broken UI can go in directly.
Prompts to steal
Tuned to this model — click any line to copy.
About GPT-5.3 Codex
GPT-5.3 Codex is OpenAI's coding specialist, announced on 5 February 2026. It combines the coding strength of the Codex line with the general reasoning and professional knowledge of the wider GPT-5 series, and OpenAI's framing of it is deliberately broad: Codex moves from an agent that writes and reviews code to an agent that can do most of what a developer does on a computer.
That shows up in what it is tuned for. Debugging, deploying, monitoring, writing specs, editing copy, tests and metrics are all in scope, not just producing a function on request. It sets high marks on the benchmarks that measure real repository work rather than puzzle-solving — SWE-Bench Pro and Terminal-Bench in particular — and OpenAI reports it runs roughly 25% faster than GPT-5.2 Codex, which matters more than it sounds when a model is doing dozens of steps in a row.
It exposes adjustable reasoning effort, so the same model can answer quickly or think hard depending on what the task deserves, and it takes images as input, so a screenshot of a broken build or an unreadable chart can go straight into the thread. The context window runs to about 400K tokens with up to 128K tokens of output, enough to hold a large slice of a repository plus a long agent transcript.
On NinjaChat it is included in every plan. Pick it from the model list when the work is software, and switch to a general model when it is not.
How to use GPT-5.3 Codex
From zero to your first result in under a minute.
01
Create a NinjaChat account and choose a plan
02
Open chat and pick GPT-5.3 Codex from the model list
03
Give it the repository context, the failure and the goal
04
Ask for a plan first on anything that spans files
Tips for better results
- Paste the real error output rather than describing it
- Say explicitly which files are in scope
- Attach a screenshot when the bug is visual
- Switch to a general GPT-5 model for non-coding work
GPT-5.3 Codex vs the alternatives
Where it wins, and where it doesn't.
vs Kimi K2.7 Code
ViewOpenAI's reasoning-effort control and wider tooling
Kimi K2.7 Code is open-weights and cheaper per token
vs GPT-5.6 Terra
Tuned specifically for software and agent runs
Terra is the better all-round generalist
Questions, answered.
Beyond chat — images & video
The same subscription covers the image studio and video generation.
GPT-5.3 Codex, and 50 more.
One subscription covers every model on NinjaChat, GPT-5.3 Codex included.
