[R] Extreme Sudoku as a constraint-satisfaction benchmark, solved natively without tools or CoT or solution backtracking

I came across an interesting writeup from Pathway that I think is interesting as a reasoning benchmark than as a puzzle result. They use “Sudoku Extreme”: about 250,000 very hard Sudoku instances. The appeal is that Sudoku here is treated as a pure constraint-satisfaction problem: each solution is trivial to verify, hard to bluff and the task isn’t naturally linguistic.