Classical Variation

With both sides castled, the Classical Variation is the central position of the Rubinstein System. Black has finished developing without committing to ...cxd4, so White must choose how to target d5. The modern main move is 9. Bg5, the Carlsbad Variation, which pins and pressures the f6-knight that guards d5. Its central line is 9...cxd4 10. Nxd4 h6 11. Be3 Re8, after which 12. Rc1 Be6 is the Chandler Variation, while 11...Bg4 is the Spassky Variation and the earlier 10...Re8 is the Petursson Variation. Black can also avoid the isolani altogether with 9...c4, the Advance Variation, or play 9...Be6, the Endgame Variation.

The immediate 9. dxc5 is the most common choice in online play. It fixes the isolani directly, and 9...Bxc5 10. Na4 (the Réti Variation) aims to trade off Black's dark-squared bishop. Black can instead answer 9...d4, the Classical Tarrasch Gambit. 9. Bf4 is a less frequent alternative. The engine gives White a slight edge, but results in practice are fairly close.