How are Sudoku variants different from standard Sudoku?

Standard Sudoku is a number game played on a 9×9 grid where the objective is to place the numbers 1–9 exactly once in each row, column, and 3×3 subgrid using logic.1

Sudoku variants differ from this standard format by introducing additional constraints or altering the grid structure to increase complexity or change the solving experience. Common variations include:1

• Constraint Variations: Puzzles where diagonal entries must be unique, specific cells are restricted to odd or even numbers, or "killer" versions where groups of cells must sum to a specific total.1
• Structural Changes: The standard 3×3 subgrids may be replaced by different 9-cell shapes, or the grid size may be expanded to 16×16 or 25×25.1
• Alternative Formats: Some variants use letters instead of numbers to form words, utilize interlinking grids, or are presented as three-dimensional 3×3×3 cubes.1

While standard Sudoku relies purely on logical placement, these variants often incorporate additional mathematical or pattern-based rules to challenge the solver.1