Three Knights Variation

The Three Knights Variation, 4. Nf3, is White's second most frequent answer to the Grünfeld. White neither releases the tension with 4. cxd5 nor commits a bishop at once. Instead the kingside knight comes out, and White keeps a choice between sharp systems with Qb3 and e4 and quieter schemes built on e3. Black almost always replies 4...Bg7. The occasional alternatives are 4...dxc4 and 4...c6, the latter reaching the Schlechter Variation of the Slav. The engine gives White a slight edge, and White scores a little better than Black on Lichess.

After 4...Bg7 the branches are defined by White's fifth move. The Russian Variation, 5. Qb3, is the most forcing. The Burille Variation, 5. e3, is the restrained option; after 5...O-O White chooses between 6. Bd3, the Paris Variation, and 6. Qb3, the Vienna Variation. The Hungarian Attack, 5. Bf4, develops the bishop outside the pawn chain, and 5...O-O 6. e3 is the Hungarian Variation. The Petrosian System, 5. Bg5, aims the bishop at the f6-knight. The Byrne–Fischer "Game of the Century" of 1956 reached the Hungarian Attack by transposition, via 1. Nf3 Nf6 2. c4 g6 3. Nc3 Bg7 4. d4 O-O 5. Bf4 d5, and continued 6. Qb3.