Speculation is a spectrum, and there's a probability attached. Consider these companies make it a rule to shit on IP as a concept.
If anyone, anywhere, would be doing this, it would be Anthropic and OpenAI. That doesn't mean they are, but that, to me, certainly pushes it past simple speculation.
I totally get the speculative aspect. However, the entire premise of them making money off software engineering is predicated on a truthfulness of whether they use that data or not. Otherwise the Chinese models (which make no promises and do log) become more viable…
I don't necessarily think it is, because of regulatory capture. We're seeing Anthropic and OpenAI try to squeeze the chinese in the courtroom more and more, and I think it's to your point: they're all doing the same things, so now they need to employ extra-business tactics to get their marketshare. I think they're hoping that Chinese models become unviable because they're literally illegal, which I don't think is very far off from happening soon. Which is bad all around, but everyone is playing dirty right now.
It's absolutely speculation (unless you have specific inside information) to claim that they are doing this. It's a fact that they could be doing this.
Edit: From your other comments, you seem to be heavily insinuating that you do in fact have inside information. If you do have such information, it's not clear to me what consequences you think you are avoiding by adding this flimsy veneer of supposed deniability.
If anyone, anywhere, would be doing this, it would be Anthropic and OpenAI. That doesn't mean they are, but that, to me, certainly pushes it past simple speculation.