1:46.45 is the record. Cade Flatt came close (broke 1:47 three times) but was likely at the absolute limits of his speed (400 PR of 46.89; 600 PR of 1:17)
Quincy Wilson is only a 16 year old sophomore and has run:
21.02 for 200
33.1 for 300
45.1 for 400
1:17 for 600
1:50 for 800
I don't think it's out of the question to suggest that, assuming he hasn't peaked, this kid could rewrite the American high school record books from 400 to 800.
The records are 44.69 (Darrell Robinson), 1:15.6 (Will Sumner), and 1:46.45 (Michael Granville)