how exactly can you assume they have unit profitability

Plenty of analysis on this point, the inputs are not secret. Check out Semianalysis for example.

They have something like 70% margin on inference.

They had 40% margin on inference in 2025.

https://archive.is/aKFYZ

You can quibble about the exact numbers, but I think it’s fairly clear at this point that inference is profitable with decent margins. Like you say, unit economics are more interesting than the profitability of the company as a whole.

so speculation from a semiconductor website. that's incredibly likely to be wrong

I think you should do a bit of research and come back once you have fixed your knowledge gaps.

what research? it's private and there is large incentive to lie until ipo

We will see once Anthropic releases their S-1 too this summer.