[This article was first published on Getting Genetics Done, and kindly contributed to R-bloggers]. (You can report issue about the content on this page here)Want to share your content on R-bloggers? click here if you have a blog, or here if you don't. Reposted from the original at https://blog.stephenturner.us/p/codex-positron.Last month I wrote about agentic coding in Positron using Positron assistant, which uses the Claude API on the back end.Positron Assistant: GitHub Copilot and Claude-Powered Agentic Coding in RStephen Turner·Jul 16Read full storyYesterday OpenAI announced a series of updates to Codex, the biggest being an IDE extension to allow you to use Codex in VS Code, Cursor, Windsurf, etc. More details at developers.openai.com/codex. And Codex is available in the Open VSX Registry, meaning you can install it in Positron.Demo: creating an R package with CodexI tried doing the same thing here with Codex as I did with Positron Assistant in the previous post. I used usethis::create_package() to give me a basic package skeleton, then I fired up Positron, hit the Codex extension in the side panel, and gave it a simple prompt.write a simple function in this R package to reverse complement a DNA sequence (i.e. A>T, C>G, G>C, T>A). Document it with Roxygen, and write unit tests with testthat. Do not add any external package dependencies other than testthat.Then I sat back and watched it work.As you can see, after running devtools::document() and devtools::test(), my tests failed. I asked Codex to fix those tests. I had to do this twice, and the second time around it’s running those tests locally and diagnosing what’s happening.The third time around all my tests pass.And devtools::check() yields no errors, warnings, or notes.The code is on the same GitHub repo, on the codex branch.Why Codex instead of Positron Assistant?I haven’t used either agent enough to know their failure modes, and which might be better in certain circumstances. As of last week, GPT-5 seems to outperform Claude for writing R code, and Codex uses GPT-5 under the hood.Another factor might be cost. Instead of using API credits, Codex uses your existing ChatGPT Plus, Team, Pro, Edu, or Enterprise subscription. In my post on Positron Assistant I showed that the entire package development experiment (admittedly simple) cost about $0.09 cents. But if you’re relying on this daily and using it for heavier tasks, you might run up a decent bill. If you’re already paying $20/month for ChatGPT Plus, using Codex doesn’t cost you any more.Finally, there’s the original selling point behind Codex before it was ever available in an IDE: You can wire up Codex to your GitHub account and ask Codex to read, write, and execute code in your repositories to answer questions or draft PRs. I haven’t tried this yet, but you can read more at developers.openai.com/codex/cloud. Getting Genetics Done by Stephen Turner is licensed under a Creative Commons Attribution (CC BY) License.To leave a comment for the author, please follow the link and comment on their blog: Getting Genetics Done.R-bloggers.com offers daily e-mail updates about R news and tutorials about learning R and many other topics. Click here if you're looking to post or find an R/data-science job.Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.Continue reading: Using OpenAI Codex in Positron