It's no secret that Barber quarters are our favorite coin series at DLRC. David Lawrence published his first book back in 1990 on the Barber quarter series and the 1901-S has always been the crown jewel of any BQ collection. We have handled literally dozens of 1901-S quarters in every grade from Poor-1 to the finest known MS68+.
With that said, we have NEVER owned an AU55! Period. This PCGS AU55 knocked our socks off. It's basically pure white with the same amount of luster we'd expect on an MS63; in fact the reverse is fully MS63, or better. The obverse is also technically mint state but has some evidence of very lightly lines we suspect from old-time album pages that slid across it a few times. It is quite simply the nicest AU 1901-S you will ever see.
CAC agrees with that assesment, as this coin is the ONLY AU example they have ever stickered. In fact CAC has not approved any 1901-S quarter between the grades of VF30 and MS63! Don't let this great coin get away!