In the standard line (1 c4 Nf6 2 Nc3 e6 3 e4 c5 4 e5 Ng8) black retreats his knight, thus occupying two of the first four moves with a maneuver that offers literally no development. this seems very unusual and I'm struggling to figure out the compensation. has white overextended and weakened his position in order to get a development advantage? I'm not quite seeing it
Though it looks scary, it appears Black could have enough resource to equalize. White's advanced space seems tough to hold and Black looks like he can initiate enough exchanges without losing position to get pretty close to equal. Though it might be Black has to play very accurately.
Seirawan - Beliavsky 1989 might be a good example of Black's idea of exchange.
Giri - Dubov 2016, which is pretty close to Korchnoi - Timman 1991, Black again looking for exchanges and relatively solid structure though in a different, maybe more scary way.