Not sure when those capabilities will be retrofit to existing ships... the golden fleet is a new concept, with the Defiant being the first ship of the fleet. Reading between the lines, it seems we have some ship defenses for hypersonic attacks, that have already been tested and have successfully "shot down" a hypersonic missile - if you believe the reports...and that was in controlled test conditions, not actual combat.
The Defiant will have the most advanced ship self-defense systems, though defense is listed as its third primary mission; these systems are designed to be modular, and more easily upgraded into ships designed for these modular systems...
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