Hypersonic glide vehicles are measures that strengthen MAD, not try to defeat them. And yes, they did beat the US to it. The purpose for HGV development was to evade ballistic missile defences.

It's not clear whether Russia actually has an operational HGV capability, or not.

For the record, it's also not clear with Status-6 is operational, either. But the technology behind Status-6 is pretty much all stuff that we already know they have working, whereas HGVs maybe not so much.

It was a disinformation campaign about hypersonic missiles.