New model in town! GPT-5-Codex is a version of GPT-5 specifically realized for agentic coding in Codex. Here’s what you need to know:

• It dynamically adapts its thinking based on the complexity of the task.
• Adheres to AGENTS.md instructions.
• It has been trained specifically for conducting code reviews and finding critical flaws.
• GPT-5 and GPT-5-Codex achieve comparable accuracy on SWE-bench Verified (72.8% vs. 74.5%), but GPT-5-Codex shows a clear advantage in code refactoring tasks (51.3% vs. 33.9%).
• OpenAI found that comments by GPT‑5-Codex are less likely to be incorrect or unimportant: GPT-5-Codex produces fewer incorrect comments (4.4% vs. 13.7%) and more high-impact comments (52.4% vs. 39.4%) than GPT-5. Interestingly, GPT-5 makes more comments per pull request on average (1.32 vs. 0.93), but with lower precision and impact.

Many are complaining about the naming and the “Codex everywhere”. Honestly, I don’t care so much about the poor naming scheme as long as models and tools are good.

GPT-5-Codex is not available in the API but it will be soon. To use it, you will need Codex CLI, so make sure to install it: npm i -g @openai/codex. @sama claims that GPT-5-Codex already represents ~40% of traffic for Codex.

I installed and tried it (yes, haven’t done before, this is the first time for me using Codex). You can choose the model reasoning effort: prompting /model, Codex will let you choose between gpt-5-codex low, gpt-5-codex medium and gpt-5-codex high. Although OpenAI recommends to leave the model_reasoning_effort at default (medium) to take the most advantage of the more dynamic reasoning effort.

Along with the model, they also provided more updates:

• Codex runs in a sandboxed environment with network access (opens in a new window) disabled, whether locally or in the cloud.
• In Codex CLI, you can now resume a previous interactive session.
• Once turned on for a GitHub repo, Codex automatically reviews PRs.
• It is possible to asynchronously delegate tasks to Codex Cloud.

And more.

I think they’re heading in the right direction, actually. They’re focusing their efforts on the tools, which is good. What’s more, I have to say that I’ve reevaluated GPT5 and am using it daily instead of Claude. That’s why I appreciate and welcome these new releases.

Last but not least, Codex is open-source!