I do think that many many labs do distill frontier models, but it's a shame that xAI also feel the need to do this - perhaps an indication or admission that in fact, they are not a frontier lab.
Because you think OpenAI/Anthropic isn't doing it? Anything that can be done to improve a model will be done, it's common sense, you think Anthropic doesn't have a shit-ton of accounts at OpenAI? common.
It feels unlikely to me that at least first few models at OpenAI/Anthropic were distilled from each other. If it is happening for newer model generations, I doubt either of them would ever publicly admit to this like Musk has done for xAI.
Indeed, they probably would never admit it, but it's common-sense because why not? It's not even illegal, it makes better models, better competitor analysis... of course Anthropic is fully aware of gpt-5.5 capacity, they must benchmark it 24/7.