The issue with hypersonic missiles is that they go so fast that the air around them heats up enough to become a plasma. This prevents radio, microwave, and infrared based comms and radar systems from working. So any proper hypersonic missile is stuck with using either optical sensors (which require a ton of processing power and is slow) or inertial sensors (which aren't very accurate due to drift) in order to plot its course.

The Russians are the only ones with "hypersonic missiles" because they're using a different definition. Theirs are just ballistic missiles that move at hypersonic speeds, which by definition can't change course and have a huge IR and radar signature, so it's not that difficult to set a slower patriot missile to be in it's way to intercept.