> So why wasn't Anthropic behind their effort?

Presumably because this was something Levent did in his spare time and because it was not obvious that this work would eventually lead to a breakthrough.

> Why did Tristan use OpenAI's models when it should have been known was a potential outcome?

I'm sure in the past he had less cynical feelings about OpenAI and their penchant for academic fraud.

> I understand they wanted a normal math collaboration but presumably what Levent brought was his resources (as far as I can see Navier-Stokes is not his speciality)

I think you're not giving the guy enough credit in saying that his contribution came down to having an API key for Anthropic models.

> Normally these things are hashed out formally beforehand to avoid the sort of thing now happening.

How would that have helped? That agreement (which may well still exist) would not have involved OpenAI.