The deepest challenge on the site
Extreme puzzles strip the grid to the fewest clues that still guarantee a unique solution. Expect long candidate chains, hidden pairs and box-line interactions before anything becomes certain. Notes are essential; the timer and your board are saved locally so you can return anytime.
Keep progressing
Warm up on Expert or Master Sudoku, study X-Wing and other patterns in the techniques hub, or try Killer Sudoku for a different kind of difficulty.