Update: in the Pando blog post, OpenAI cites GPT-6 Astra as the model used to formalize the system
In the engineering write-up “Scaling Git at OpenAI,” OpenAI itself wrote that, with GPT-6 Astra, agents wrote Lean and TLA+ to formalize a “theory of Pando,” find bugs and prove system properties. Continuous sessions ran for hundreds of hours. Until now, in previous editions, GPT-6 Astra had appeared only as a market rumor; now the name shows up in an official company engineering blog.
Source OpenAI