Historically the Specialized Crux has been the dedicated cyclocross (CX) race bike in the line, while the Diverge is the go-to gravel bike. It seems that Specialized is changing it up, and the new 2021 Crux got a gravel facelift, and an Aethos facelift. All Crux models are geared for gravel and rolling on 38mm tires with updated geometry to be more gravel friendly. The frame is essentially an Aethos for off-road with geometry that is still very race-oriented.
The bottom bracket is lower, the front slacker and the wheelbase has been lengthened, still offering a solid CX rig but much-improved gravel ability. Think of this as the bike for the pointy end of an event. Specialized still believes that the Diverge is the bike for most, but this is a much better option for those that want quicker handling and might dabble in the local CX scene.
For more info, head to Specialized.com