GPT-5.2-Codex Specifications and Adoption: Do Not Invent a Performance Review
A source-checked guide to GPT-5.2-Codex specifications, pricing, supported features, and a safe evaluation plan without claiming unperformed benchmarks.
3 min read
Correction added July 26, 2026: The previous version labeled unmeasured claims about context retention and accuracy as a review. This version separates official specifications from a test plan for your own repository.
Conclusion: Specifications are known; repository performance is not
OpenAI describes GPT-5.2-Codex as a GPT-5.2 variant optimized for agentic coding in Codex and similar environments. The official model page documents context, maximum output, supported inputs, reasoning levels, and API prices. GPT-5.2-Codex model page
That documentation does not prove that the model will refactor your codebase reliably or diagnose your logs correctly. Those outcomes require local evaluation.
Specifications checked July 26, 2026
| Item | Official listing |
|---|---|
| Model ID | gpt-5.2-codex |
| Intended use | Long-horizon, agentic coding |
| Context window | 400,000 tokens |
| Maximum output | 128,000 tokens |
| Knowledge cutoff | August 31, 2025 |
| Reasoning effort | low, medium, high, xhigh |
| Input | Text and images |
| Output | Text |
| API price | $1.75 input, $0.175 cached input, and $14 output per million tokens |
Prices and availability can change. Recheck the model and pricing pages immediately before use. ChatGPT plan access and API token pricing are separate concerns.
Evaluate with three fixed repository tasks
| Task | Success condition | Record as failure |
|---|---|---|
| Small bug fix | Adds a reproduction test and keeps the existing suite green | Hides the symptom or changes unrelated code |
| Mechanical refactor | Preserves the public API and passes type checks | Changes behavior or misses references |
| Multi-file feature | Meets acceptance criteria and passes an integration test | Claims completion with missing behavior or weaker tests |
Record success, elapsed time, tokens, retries, and the lines a human had to repair. Run the same tasks with the current workflow or comparison model before claiming an improvement.
Design permissions separately from model quality
Codex may edit files and run commands. OpenAI's security guidance treats sandboxing and approvals as part of the trust boundary. Agent approvals and security
- Start with limited write scope and network access.
- Require review before deletion, external sends, credential access, or production changes.
- Inspect the diff for unrelated or overwritten user work.
- Run the existing test suite and static checks, not only model-authored tests.
- Keep secrets out of prompts, logs, and repositories.
What this article did not test
This revision did not benchmark GPT-5.2-Codex. It therefore does not claim superior long-task memory, design judgment, or vulnerability detection.
Adopt it only after measuring the target repository with fixed permissions, tests, and a cost ceiling.
Primary sources checked
Important claims should also link to the relevant source in the article body.
- GPT-5.2-Codex ModelOpenAI · official-documentation · Checked: 2026-07-26
- Agent approvals and securityOpenAI · official-documentation · Checked: 2026-07-26