In case you are not aware, the actual theorem statement of N-S was never translated by an LLM, but was written independently by formal conjectures, as they say in the README [1].
A Lean proof has a much higher probability of being correct (in my opinion) than any published (either preprint or peer-reviewed) paper, yet no one before LLMs were walking around claiming every result published can't be trusted yet (without an actual reason).
We have seen one such instance of Lean bugs, which was found adversely against Lean (as in find bug then use this bug to prove Collatz, not just found when being asked to prove it).
It's also worth to note that the way N-S (and all the other proofs by OpenAI etc) have been found is first prove it in NL then translate to Lean. I.e. it would have to first believe it found a correct proof in NL, and then afterwards either accidentally or on purpose use a Lean kernel bug.
edit:
Probably also worth to mention that the proof have been checked both by the Lean kernel and the independent nanoda kernel, so it would need to exploit bug(s) from both.
2. No exploit of a kernel soundness bug in Lean (and the independent kernel nanodo, which OpenAI also checks against).
In particular, if you trust this, then you don't need to care about anything else the Lean program does, no matter how many lines, lemmas etc. it makes along the way.
As I said above, the theorem statement have been written independently by formal conjectures, and you are free to read it yourself (or trust other people have done it).
So, assuming you don't disagree the theorem statement have been written correctly, you pretty much need to believe 2 is false, if you don't trust the proof [1]. And that's what I find has a rather low probability personally.
[1] As the book says, you also need to trust the hardware, firmware etc.
A Lean proof has a much higher probability of being correct (in my opinion) than any published (either preprint or peer-reviewed) paper, yet no one before LLMs were walking around claiming every result published can't be trusted yet (without an actual reason).
We have seen one such instance of Lean bugs, which was found adversely against Lean (as in find bug then use this bug to prove Collatz, not just found when being asked to prove it).
It's also worth to note that the way N-S (and all the other proofs by OpenAI etc) have been found is first prove it in NL then translate to Lean. I.e. it would have to first believe it found a correct proof in NL, and then afterwards either accidentally or on purpose use a Lean kernel bug.
[1]: https://github.com/openai/NavierStokesAndEuler/blob/main/Com...
edit: Probably also worth to mention that the proof have been checked both by the Lean kernel and the independent nanoda kernel, so it would need to exploit bug(s) from both.