Indian Defense: Accelerated London System: what to play after Bf4?

In the Indian Defense: Accelerated London System (ECO A45), Black faces an immediate development of White's dark-squared bishop to f4. The engine's top-ranked choice is d5, evaluated at +0.08, which stakes an immediate claim in the center and mirrors White's pawn structure. Other primary responses include e6 and g6, both offering Black solid setups against the London framework.

Central Contestation with d5

The move d5 occurs in 28.6% of recorded games (9.48M recorded) and results in White scoring 52.1%. By establishing a central pawn on d5, Black prevents White from achieving an uncontested central presence while setting up standard queen's pawn structures. An illustrative continuation from the engine runs d5 e3 c5 Nf3 e6 Nbd2, where Black quickly strikes at White's base with a pawn push to c5.

Kingside Setups with g6 and e6

The most frequently played option in the database is g6, appearing in 37.4% of games (12M recorded) with White scoring 49.7% and an engine evaluation of +0.12. This King's Indian-style fianchetto is shown in the line g6 Nf3 Bg7 e3 d6 c3, aiming to challenge White's setup with a solid kingside structure. Alternatively, e6 is chosen in 31.9% of games (11M recorded) with White scoring 52.0% and an evaluation of +0.09, often proceeding via e6 e3 c5 Nd2 d5 Ngf3.

Minor Alternatives

Less common choices include c6, played in 2.1% of games (697K recorded, evaluated at +0.28, White scoring 50.7%), which can lead to c6 Nd2 Nh5 Bg5 Qa5 Nf3. The engine also recognizes a6 at an evaluation of +0.25, continuing into a6 Nf3 d5 e3 e6 Nbd2.