I believe this is exactly what is happening. US DoD, and whoever else is buying.

I have heard several experience reports from users of GPT 5.6 Sol and Fable 5 that the models are tenacious to the point of being kind of hard to use for actual productive work.

It seems like the main use cases are: crushing benchmarks, long-horizon lightly-attended research loops (such as training a frontier LLM), and hacking.