The US Air Force Nuclear Weapons Center has released, likely accidentally, a list of notes on ideas for potential ICBM upgrades, which included a hypersonic glide vehicle, the first suggestion that the US military is exploring hypersonic nuclear weapons.
Analysts have expected hypersonics to be a trigger for a potential arms race, with Russia having already worked on the matter as a potential counter to the US withdrawing from the INF Treaty, which could lead to US nukes in Europe.
Though the US has less obvious use for hypersonic arms, such arms would increase first-strike capabilities and getting first strikes on the ground in enemy territory before retaliation can be ordered has long been a priority.
These gliders may be decades down the road, and may never be a priority for the US at all. It’s a cinch that if there is a New START replacement, it would limit both sides on hypersonics to prevent the arms race, and to prevent weakening the already limited missile defense systems.