According to a news article on Russia Today, Russia is leading the US in hypersonic missile development by generations:
The bottom line is that Russia – in terms of hypersonic missile development – is about four generations ahead of the US, if we measure it by the development of the S-300, S-400 and S-500 systems. As a working hypothesis, we could describe the next system – already in the drawing boards – as the S-600. It would take the US military at least ten years to develop and roll out a new weapons system, which in military terms represents a generation.
Does it warrant credence of their conclusion, Russia being immune to (conventional) military retaliation?
The key fact of the matter needs to be stressed over and over again; the S-500 is impenetrable - and allows Russia for the first time in history to launch a first strike nuclear attack, if it ever chooses to do so, and be immune to retaliation.