Fianchetto Defense, Euwe Variation

The Euwe Variation, 4...c5, has Black strike at d4 immediately instead of castling first or occupying the center with 4...d5. The c-pawn adds to the pressure that the g7 bishop already exerts on the long diagonal. White most often answers 5. e3, which keeps the standard buildup. The alternative 5. c3 reinforces d4 directly, and 5. Bxf6 gives up the bishop pair to remove the f6 knight. The engine considers the position roughly balanced, and the line is seldom played.