Kieseritzky Gambit, Berlin Defense, Rubinstein Variation

The Rubinstein Variation, 6. d4, is regarded as the main line of the Berlin Defense. Rather than resolve the mutual attacks on g4 and e4, White adds central support and opens the c1-bishop's diagonal toward f4. After 6...d6, by far the most common reply, the knight can drop back to d3 without obstructing the d-pawn, unlike 6. d3, which also hems in the f1-bishop. Engines give Black a slight edge.