Legendary 16x16 Sudoku — The Hardest Giant Grids

Legendary 16x16 sudoku is rated 10.0 and above, the top band on the site and the hardest 16x16 sudoku we offer. Ordinary tools run out here, and nets or trial-and-verify reasoning appear. It suits experienced solvers who want the hardest giant puzzles we have and can spread a solve over days.

What this level asks

Everything below it, plus endurance. Legendary puzzles keep fewer givens than easy ones (94 of 256 on average against 151, per our catalogue), and the hardest 16x16 puzzle we have is rated 10.4. The deductions are long and the grid is large.

Techniques you will meet

• Forcing nets (from 8.5): branching assumptions that must all agree.
• Bowman's Bingo (from 7.5): assume a candidate and follow singles until the grid contradicts itself, which removes it. This is the last-resort tier.
• Almost locked sets: groups of cells one candidate short of a locked set.
• Alternating inference chains: long chains of true and false links.

Treat each assumption as a small experiment. Write it down, follow its consequences, and look for either a contradiction or a conclusion shared by all branches. On a 256-cell grid a contradiction can take many steps to appear, so keep each trial short and undo it cleanly. If nothing works, a missing or stale candidate is more likely than a technique you lack, so rebuild the notes in the most crowded unit and start again.

Tips for this level

• Exhaust every simpler technique before trying a net.
• Keep a written record of each assumption and what it forced.
• Split the solve across days. Autosave keeps every move.

Next step

Step back to master 16x16 for a gentler climb, or read the hardest sudoku puzzles for what sits at the very top.