Why do we even reasonably need something this fast?

Wouldn't it be much more cost-effective to merely link up with strategic partners in other countries (Germany / Israel; Philippines; etc.) to give us the distribution we need for "conventional" missiles that would hit in the same timeframe?

Missiles can be shot down by state actors, non-state actors can hide deep in areas which are out of range of the U.S. or its allies. But launching anything on an ICBM makes it almost impossible for other nations to distinguish from a nuclear missile launch.

Of course, if Prompt Global Strike is capable of carrying cargo with it then maybe countries like Russia or China would suspect it can also carry a small nuclear warhead, so it may be that concern doesn't completely go away.

I don't think it's in any country's interest to do a nuclear attack with anything but a blow that would cripple response, a small nuclear warhead seems like an invitation to go from tolerated and accepted to hated.