If your chicks are from male breeders with slow feathering and female breeders of fast feathering, you can do feather sexing. Else, wait two weeks and the boys will have red combs! Some start to show as early as 4-5 days!
I looks like a pullet to me. Only because our white leghorn roosters seemed to grow waddles and combs longer and faster. Here's a longhorn gen in front and roo in back. The hen still has a red comb larger than other breeds.