The rules of Hyper Sudoku

Hyper Sudoku is classic Sudoku with four extra regions. Same 9×9 grid, same digits 1 through 9, same rows and columns and 3×3 boxes — and then, on top of that, four additional 3×3 shaded regions sitting inside the grid, each carrying the same uniqueness rule that rows and columns and boxes do. The variant is also called Windoku, after the Dutch puzzle-magazine NRC where it first appeared, and the two names refer to the same puzzle.

The constraint set

If you know classic Sudoku, the first three rules are familiar. The fourth is the addition that makes Hyper Sudoku what it is.

1. Every row contains the digits 1 through 9, each exactly once.
2. Every column contains the digits 1 through 9, each exactly once.
3. Every 3×3 box contains the digits 1 through 9, each exactly once.
4. Each of the four hyper regions — the shaded 3×3 blocks at positions (2, 2), (2, 6), (6, 2), and (6, 6) — contains the digits 1 through 9, each exactly once.

That's the whole puzzle. Four extra units, each one structurally identical to a box, each one obeying the same rule.

Where the hyper regions sit

The four shaded 3×3 regions are arranged symmetrically inside the grid. Each occupies a 3×3 block whose top-left corner is at row 2, column 2; row 2, column 6; row 6, column 2; and row 6, column 6. The regions don't touch each other and don't sit on the grid edges. Each hyper region overlaps four of the nine standard 3×3 boxes — every cell of every hyper region belongs to a standard box as well, just as it belongs to a row and a column.

On Sudoku Mountain's board, the hyper regions are marked with a subtle coral outline so you can see at a glance which cells participate in the extra constraint. There are 36 cells in total inside hyper regions — nine per region, four regions, no overlap.

What changes mechanically

In classic Sudoku, every cell belongs to three units: a row, a column, and a 3×3 box. In Hyper Sudoku, the 36 cells inside hyper regions belong to four units instead. That's the only change. The other 45 cells — the ones outside the hyper regions — play exactly as they would in a classic Sudoku.

The technique vocabulary is unchanged. Naked singles, hidden singles, naked pairs, hidden pairs, locked candidates, X-wings, every move that fires in classic also fires in Hyper. The hyper regions just give the techniques more units to fire on. The one move that's genuinely specific to the variant is the hyper-only cell — a cell whose digit is forced by its hyper region alone, even though no row, column, or box uniqueness would have placed it.

Why four regions, and why those positions

The four hyper regions are positioned so that every cell inside one of them sits at the intersection of a box and one neighbouring corner of the grid in each direction. The result is a Sudoku where the extra constraint is densest in the middle of each quadrant of the board and absent at the edges. This is a deliberate design choice — it puts the extra reasoning load where the classic puzzle would otherwise have the least constraint, balancing out the difficulty across the grid.

Where the rule pays off

The hyper regions help most in the early-to-middle solve. Because each hyper region overlaps four standard boxes, a single placement inside a hyper region often constrains digits across a wider swath of the board than a placement in a corner box would have. The puzzle tends to feel more connected than a classic of the same tier — placements ripple further.

If you'd like to try one, our easy Hyper Sudoku puzzles are the right entry point. The rules are easy to absorb on the first puzzle; the tactical wrinkles take two or three more.