According to Entertainment Weekly:


"Alien: Romulus is set between the events of Alien and Aliens, and Alvarez was a stickler for communicating that through specific details. The gun that Spaeny is wielding in the photo above, for instance, is meant to be halfway between the flamethrower Ripley wielded against the original Xenomorph and the pulse rifle used in Aliens.

The same scrutiny was applied to the Xenomorph’s design, which Alvarez promises is closer to H.R. Giger’s original creation than any other iteration."