Yea so the universe says nothing can move faster than a massless particle in a vacuum. The photon is the most famous—hence the speed of light—but any massless this can move at it. So GWs do theoretically move at the speed of light, though checking to see if they do requires a lot of analysis and is tricky to figure out. But yes theoretically they do move at the speed of causality (or the speed that things happen in the universe unless someone slows them down) I’m a physicist who’s now listened to a ton of LIGO’s founders talk about it.