What's the lightest complete road bicycle that meets UCI requirements (except possibly being too light)? I've seen various claims over the years, but which manufacturer holds the record, today?

Also, what size bike and which components go with the claim?

Happy to hear about "custom" / "one-off" vs. (mass) production, but for one-offs it'd be great to know there's proof that the bike is race-proven or otherwise structurally sound.
GCN did a piece a little while ago on a 4.28-kg bike. The frame is a Cannondale, but everything has been customized to get the weight down, including stripping the paint from the frame and replacing all the bolts with carbon-fiber equivalents (I hadn't even known there were carbon-fiber bolts!).