This is from a Shimano Rep:
Our traditional road cranks have a Q-factor of 146mm, so the GRX line up will increase to 2.5mm on each side, bringing Q-factor to 151mm. However, we make a new XTR pedal that features a -3mm spindle on each side, so you could narrow the gap back to your road setup.
Mike
1x and 2x are both 5mm wider in total. So 2.5mm on each side (I measured it with a caliper). I’ve put two 1mm pedal spacers on my left sided power meter.
Power2Max recently released a new gravel power meter that has the option to run an offset chainring to be compatible with the GRX front derailleur.
Obviously it wouldn’t be compatible with GRX cranks but it should work great with the rest of the groupset.
I’m running an Easton crankset on otherwise full GRX 2x groupset. I was recommended by P2M to use the NGeco MTB Race Face single power meter. Can you elaborate what kind of issues others have had with them?
I swapped out the grx left side crank on my canyon grail with an ultegra stages pm, and it works fine! it was able to clear the chainstay no problem.
After waiting for many months, I was finally able to buy the stages left sided GRX powermeter @competitive cyclist. Was looking around all summer 
4iiii just released the option for a left side, ride ready PM. So you can just buy the crank, no factory install needed.
Just put my 105 4iiii crank onto my GRX worked like a dream, didn’t notice the offset difference. Biggest problem was I got a puncture 
I’ve now added a spacer to the pedal to offset 1mm to see if it any better. For those wearing SPD shoes and only one bike you could simply adjust the cleat on the left shoe to account for the offset.
There’s definitely a correlation here - the bike police will forever curse you for mixing group sets.
Lol
Fun times to be in the market for a gravel power meter! I’ve read through this thread and have zeroed in on a couple power meters of interest for which I’d love feedback.
I recently bought a Giant Revolt Advanced 2, which comes with all GRX except the Praxis crankset. I’d like to install a dual-sided power meter and based on reading through this thread have zeroed in on two main options:
Am I missing something an obvious option? Appreciate the feedback .
Not really missing something but just make sure you have enough clearance on the chainstay for the powermeter pod / a crank with a different Q factor.
Q: are the GRX front mechs OK with non-GRX cranksets that have the lesser (ie normal, road) offset? ie. is there sufficient adjustability to wind them 2.5mm inboard from where they would be if you were using GRX cranks.
I assume it’s all fine, if that’s what you were already doing; just asking for my own interest really…
Yeah I’m not sure a crank with the additional 2.5mm offset will work very well with a non GRX crank. Saying that I haven’t seen any reviews of the 4iii option on a GRX, let’s hope it’s more accurate than on other Shimano cranks. Actually just looked at the power2max website and it states it has GRX offset. Despite the difference I think I’d go with power2max if I could afford the difference. Also don’t forget the I don’t think the $500 for 4iii includes the cranks.
the GRX cranks don’t use the same crankarm construction as the R8000 and R9000 granks. GP Lama said he wouldn’t the GRX cranks to suffer the same issue.
Stuart, you posted that as a reply to me but I was asking a different question… 
I was wondering if there’s any issue (probably not, but just checking…) using a GRX front mech (FD) with a regular offset crankset, where its small chainring would be 2.5mm inboard vs. a GRX crank’s small chainring - essentially whether there’s sufficient inboard adjustability in the GRX FD to run smoothly in the lowest gear combo of a regular crankset.
Whoops, regular offset crank. I believe it won’t work or at least not brilliantly.
This is reply I received from Power2max when I asked them this same line of questions:
No, road chainline and q factor are independent. Q factor is how wide the spindle is. Chainline is the offset of the spider/powermeter. You can have either chainline with either front derailleur but it is recommended by shimano to run road chainline with road front derailleurs and GRX with GRX. But both are interchangeable. We don’t sell any non road q factor cranks. You want to choose GRX chainline/spacing if that’s what you are running.
Hey there guys, I have just ordered a Trek Checkpoint ALR 5 with GRX 810. I have a Quarq D Zero road power meter crank with 50/34 rings, is this likely to work with with the GRX front derraileur (if I swap the BB to GXP)? Is anyone running this setup?
Thanks in advance!