Czech Variation, with Nf3

This line is the Czech Variation of the Old Indian Defense in its 3. Nf3 form. After 1. d4 Nf6 2. c4 d6 3. Nf3, Black delays both ...Nbd7 and ...e5 and plays 3...c6 instead. The pawn takes d5 and b5 away from White's pieces, supports a later ...e5, and keeps open a queenside advance with ...b5, while the queen gains access to the a5–e1 diagonal and the c7 square. The same position can also come from 1. d4 Nf6 2. c4 c6 3. Nf3 d6, a move order that turns a potential Slav into an Old Indian.

White's usual answer, chosen in about two-thirds of games, is 4. Nc3, which brings the knight to its natural square and prepares e4, leading to the familiar space-versus-solidity structures. The fianchetto with 4. g3 is the main alternative, and 4. e3 is a quieter option that scores poorly for White in practice. The engine gives White a slight edge, and on Lichess White scores a little better than Black. The play is mostly maneuvering rather than forcing.