Well, first the AIM-260A is the correct name of the missile in question. Sometime in March, 2021 I happened by a hanger and saw the missile up close. I'm not willing to share further information, you'll just see that what I've shared is accurate when they make some official announcement. Cool stuff, really.
Oh, please. Yes, each variant of a missile or plane gets a suffix letter, but we still talk about the whole family by the base designation. No one has ever won a dispute with "actually it's F-15A not F-15."
More fundamentally, you say you just happened to see a sensitive, non-public missile while wandering (unescorted, apparently) around a USAF hangar. Either you're bullshitting or you're violating your NDA. I know which way I'm guessing, but either way, you should probably stop talking now.