One key consideration that I only got recently is the difference between a cruise & ballistic missile. A ballistic missile launches at great velocity, then more or less falls at it's target (over an extended distance) using a ballistic trajectory. A cruise missile is under power for a large part of it's journey, typically flying much lower, & able to navigate/direct itself.
A ballistic missile is often quite supersonic. But cruise missiles being hypersonic is definitely a big shift.
I was pretty surprised by how slow cruise missiles are when I read up on them recently - similar to big airliner speeds. I always had a mental image of missiles as these "fastest in the sky" things that you could only dodge but not outrun. It's possibly true for Sidewinders but even they top out around Mach 2.5, so the hypersonic developments are a huge step forward.
Still kinda surprised there aren't fast missiles that use rocket engines. It works for ICBMs? I don't see a reason they couldn't maneuver as well. Maybe the hypersonic regime makes things novel not just for propulsion but control too.
Most missiles do use rocket engines. Solid rockets are much easier to store and use than liquid fueled engines, whether rocket or turbojet. They can get pretty fast, too: the AMRAAM is supposed to go mach 4. The downside of any rocket engine is that the fuel and oxidizer run out quickly; the AMRAAM goes that fast in order to have a long range, as the motor burns out fairly soon. A few newer air to air missiles, like the British Meteor, have air breathing liquid fueled turbojets in order to increase range. Cruise missiles with their air breathing engines are the odd one out in missile tech.
Rocket engines require onboard oxidizer (or equivalent), so you have to carry a substantial additional amount of mass along with you.
Air-breathing engines are able to save all that mass by using atmospheric oxygen.
This matters, because it's the rocket equation in reverse: no onboard oxidizer = lighter vehicle = less fuel needed = even lighter vehicle = longer range / more payload
this is a good queue-in to start talking about mass ratio: the ratio of weight that is dedicated to payload versus the weight of the delivery platform and it's fuel (slightly simplified take).
this device is almost certainly air breathing. there's simply too big an oxygen-breathing-demand at speed to do anything else for sustained high speed flight, where you need to be generating a lot of motive force.
The Standard-Missile family from the US can all go faster than Mach 2.5. But land attack missiles have never needed to be particularly fast until recently.
All ballistic missiles are hypersonic. The V-2 was hypersonic. That's because range is directly dependent on speed and you wouldn't have basically any range if you had a mere supersonic speed.
A ballistic missile is often quite supersonic. But cruise missiles being hypersonic is definitely a big shift.