Yep, it was on integrating GTA V into Universe[0].

Interestingly, that post links to a specific blog post on GTA V integration[1], but going to that link redirects to the initial "Introducing OpenAI" post[2]. I can't find the GTA V blog post[3] on their blog anymore.

Edit:

In addition, the GitHub repository[4] for spinning up a GTA V server instance from the post[3] no longer exists.

[0]: https://news.ycombinator.com/item?id=13375543

[1]: https://openai.com/blog/GTA-V-plus-Universe/

[2]: https://openai.com/blog/introducing-openai/

[3]: http://web.archive.org/web/20170112173923/https://openai.com...

[4]: https://github.com/openai/universe-windows-envs/blob/master/...