I'm happy it's not a project I'm depending on, but a large enough project had to try this at some point so that we all can learn from how it goes.
I think this is why Antropic bought bun, so that they can sell big code translation as a feature for all the banks with COBOL code that they want to get rid of for a long time.
Still, those banks / enterprises won't appreciate the number of unit test changes.
And I agree with another comment that Codex xhigh is much better for these kinds of tasks, but still hard on this kind of scale.
The MR is right there, linked at the top of this page. You can check who is telling the truth.
That said, I don't know how anyone is actually claiming to have done that. All day, the size of the MR makes the diff take too long to load and GitHub dies. I'll have to pull it later to check myself.