So Shimano dropped GRX 12-speed mechanical today - Here are my technical notes -

Shimano is billing 3 options:

2x12 = 48/31T double with 11-36 HG cassette

Basically this is the same crank gearing, but a cassette with a little more bottom end and the cassette will fit all the HG freehubs on the market 

1x12= 42T or 40T single with 10-45T microspline cassette

and

1x12= 42T or 40T single with 10-51T microspline cassette 

So, what is interesting here is the 1x groups have been expanded, for the left lever you can still get a brake only or a integrated dropper remote, these 1x groups share cassettes with XT 12-speed so, this requires a Microspline freehub, unfortunately very few wheel options right now with a Microspline freehub and 142x12 hub spacing, but there is a new GRX880 carbon wheelset ($1549) that has the Microspline freehub with 142x12 hub spacing (Shimano looking to sell more wheels?)

Also, unique here is there is a specific rear derailleur for each cassette options - with RX822-GS (short) matching with the 10-45T

RX822-SGS (long) matching with the 10-51T

For 2x there is a RX820 for the 11-36T 

All GRX 12 groups share rotors and chains with XT/Ultegra

Overall we think GRX-12  looks like a winner, we hope hub makers are paying attention so more wheel options come available for the 1x12 groups w/ the XT cassettes to fit gravel frames, but perhaps this is a non-issue as Microspline drivers have been available for a long time 

By our count, full groups came it at:

$1584.91 for 2x12 and

$1542.92 1x12 (left brake lever only) 

$1572.92 1x12 (left dropper remote) 

What do you think?