I would be surprised if the government doesn't already have AI more powerful than GPT4. There's no way anybody would obey a moratorium. It would just give one side an asymmetric advantage. The genie is out of the bottle, it's not going back in.
Discussion
I don't doubt that there's some borderline-rogue US agency (read: NSA) building something. However, the odds of the collective idiocy of the USG actually putting it to use... doubtful.