Kmoch Variation

The Kmoch Variation, 4. f3, is often called simply the 4. f3 Variation. It has also gone by the Gheorghiu Variation, after Florin Gheorghiu, who used it frequently early in his career, and the Shirov Variation, after Alexei Shirov, who had success with it in the early 1990s. Rather than breaking the pin or forcing the bishop to decide, White prepares e4 directly, seeking a large pawn center and sometimes a later e5 to dislodge the f6-knight. The price is time. The f-pawn move develops nothing and loosens White's kingside, and an overextended center can become a target for Black's pawn breaks.

Black's two main answers are 4...d5 and 4...c5. The more common 4...d5 fights for e4 along Queen's Gambit Declined lines. After 5. a3 Bxc3+ 6. bxc3 c5 7. cxd5 Nxd5, the game reaches a position that can also come from the Sämisch Variation. White usually continues 8. dxc5 to free the bishop pair and follows with e4, while Black prepares ...e5 to stop the e- and f-pawns from advancing. The flank strike 4...c5 is usually met by 5. d5, a Benoni-style structure in which Black can choose among 5...b5, 5...O-O, 5...Bxc3+ and 5...Nh5. After 4...c5, 5. a3 Bxc3+ 6. bxc3 transposes straight into the Sämisch. The engine rates the starting position as roughly balanced, and White scores slightly better online.