Master 16x16 Sudoku is rated 7.0–9.9: forcing chains and nets are required, and they must be tracked across sixteen symbols and 256 cells. This is a marathon rather than a puzzle — the kind of grid experienced solvers return to over days.
Master giant puzzles are a mix of our own rated carves and imported hardest-16x16 collections. Autosave keeps every move, so there is no need to finish in one go. Read how these variants developed in our article on giant Sudoku grids.