Knight Variation

The Knight Variation, 4. Nf3, is White's standard continuation in the accepted Vienna Gambit after 2...Nc6 3. f4 exf4. The knight guards h4 and rules out the ...Qh4+ check that defines the Steinitz Gambit. White therefore keeps the option of castling while preparing d4 and Bc4. One reference source considers it the only fourth move that holds the game near equality with best play. The engine still gives Black a slight edge. In practice, however, White scores well and draws are uncommon.

Black's three main replies are about equally popular. Both 4...Nf6 and 4...d6 develop without committing the kingside pawns, and White scores better against them. The engine's first choice is 4...g5, which holds the f4-pawn in King's Gambit fashion, and Black scores best with it. White can undermine the pawn chain with 5. g3, reaching an unclear position. White can also enter one of the sacrificial lines: the Hamppe-Allgaier (5. h4 g4 6. Ng5), the Hamppe-Muzio (5. Bc4 g4 6. O-O) or the Pierce Gambit (5. d4). A less common choice is the Cunningham Defense, 4...Be7, which has given Black slightly better results than White.