You’ll have to tell us about the ride quality, and how you liked it.

What kind of terrain do you ride with it?

• I fit 650b x 54 mm (measured tires) between the chainstays with ~2-2.5 mm of room on either side! I'm planning on running 650b x 50-52 mm as my gravel setup on new wheels, so this is very nice. I don't have fat 700c tires to test with, but I'll get more exact chainstay measurements later.
• The headset bearing cups are molded well and the provided bearings fit snugly with zero play. I'm using a Token S-Box compression ring and top cap, as I don't like the aluminum C-shaped compression ring that comes with the stock headset - too much risk of fork damage and it's HEAVY. Unfortunately, the Token bearings are 51.8mm OD and have a small amount of play in the 52.0 mm bearing seats, so I can't use them.
• The hose routing hole on the steerer tube is kind of rough, but won't be a concern when it's hidden away in the frame. There was one strand of loose carbon that I sliced off without issue. I pushed a brake hose up from the caliper end and it popped right out the steerer hole without any guidance needed, so the inside is perfectly fine.
• Speaking of the inside, the interior of the frame looks to be very well molded, without much in the way of wrinkles or excess resin. The only real exception are the areas where the chainstays are bonded right behind the bottom bracket, which have some lumpy resin but nothing major. See the endoscope pics in the album.
• There's a cable routing port on the back of the driveside seatstay, which is a far better location than the port on the underside of the chainstay. However, it looks like the seatstay port may only be large enough for electronic cables - not an issue for me since I'm building this up with Di2, but something to consider if you're going mechanical.
• There's a fender mounting boss on the underside of the fork crown. Not super useful on the holeless fork since there's no corresponding mounting holes by the dropouts - I'd like to see those holes present, but clip-on fenders should be fine for the winter.
• The bottom bracket threads are clean, with no point overspray or damage. I'm not sure if the paint around the cups will be damaged by BB installation - I'll be doing that tomorrow with a SRAM T47 BB and an Abbey tools socket, clamped to the frame, so hopefully there's not much room for anything to slip.
• The front thru-axle has measurements written on it but the rear doesn't. Ideally it would, but here's the measurements: ~168mm length, ~15mm thread length, 1.0 pitch (thanks, UDH). The brass washer on the rear axle is captive - good - but the washer on the front isn't retained in any way and just pulls straight off. Also, the rear axle head sits flush with the frame but the front axle head protrudes slightly. The axles are quite heavy, I'll likely replace them in the future.
• The flip chip on the brake side is only retained by the axle! When the axle isn't there, it just falls straight out of the fork. Not good, especially because the driveside chip is elegantly retained by a little grub screw on the tip of the fork blade - why couldn't this have been done on both sides??? This is my biggest complaint since it's so easily avoidable, and actually IS avoided on only one of the blades!
• The brake mounts on the frame and fork look to have been faced, but then not fully masked, so there's a rim of paint around the edges that prevent mounts from sitting flat and flush. I did some experiments with carefully slicing away the paint from one of the fork brake mounts, and it looks pretty good, so I'm going to complete that on all the mounts once I'm done with this post.

Where did you end up sourcing the Token headset from? I've had a look online and they don't seem to be particularly easy to find. Is it the TK1556SP model?

• With tires measuring almost exactly 50 mm, I have 4 mm clearance at the chainstays on each side. I expect the tires to stretch a little bit over time, so it's good to know that if they plump out another 2 mm I'll still have adequate clearance. I didn't bother measuring the front, there's easily >6 mm of room on either side, the fork could probably take a 2.1" tire if it's not too knobby.
  
• The total diameter (including tires) of my 650b wheels is about 1 cm less than my 700c wheels; the ~5 mm difference in radius didn't really change handling but did lower the cranks by that much, which is important because I got two or three pedal strikes, even with a decent choice of line so as to avoid the larger rocks. I'll be getting crank boots since my crankarms are carbon. Not really an issue on terrain where you're not trying to navigate through a rock field, but that does make up some of the more fun routes around here so it applies to my use case.
• Probably due to the far fatter and squarer tire profile, the handling at the front was more sedate than with the 700c wheels; it did take a bit of persuasion to rapidly change direction when I was crawling uphill. No real change with how the rear wheel tracked, though, which was nice. Overall the handling is quite stable but I wouldn't classify it as slack, certainly not on the level of a Stigmata or similarly headtube-angled frames. No problems staying upright the few times that the rear wheel broke traction, which fortunately never happened up front.

• The downtube bottle cage mounts are a bit too far up to fit a 750 ml bottle. I used a bottle cage extender (https://www.aliexpress.us/item/3256805494776538.html but the design is generic) to drop the cage about 2 cm down, which works well. I did drink all of that extra water so it's worth it.
• I didn't get any chainslap on the way up even as I was bouncing around, but did get a fair amount on the rutted dirt descent, even in the big ring and lower gears in the back. I'll be putting on another layer or two of clear tape on top of the single layer that's already on the chainstay, just for a bit more cushioning.
• Being able to run a dropper post may be the single biggest advantage this frame has over an actual Canyon Grail. The dropper is pretty much mandatory for the dirt descents I do and I also use it quite a bit to get aero on parts of descents faster than I can spin my 48/11 top gear (i.e. most of any descent). I have the clamping wedge torqued to 7 Nm and the seatpost hasn't slipped at all - I put a ring of silver Sharpie around the base to make sure - which is impressive, considering how fat I am.
• The rear rim already got a few small nicks from rocks flipping up from under the tire, but I've found with my road rims that a tiny bit of clear nail polish hides such marks on glossy carbon very well.
• The wheelbuilding process on these rims was quite nice. LightBicycle AM728 rims, i9 Torch rear hub + i9 Solix front hub (Torch hubs are effectively impossible to find now and purple ones simply no longer exist  ), Sapim CX Ray/Sprint front/rear respectively. Was my first time building with alloy nipples, Sapim Double Square, and they performed no different than the brass ones I've used before. The internal square part is easy to fit an internal tool (https://www.aliexpress.us/item/3256802115683590.html) and rotate, which is nice because it allows a spoke holder to keep the bladed spoke aligned without a spoke key in the way.

I'm using the SRAM T47 BB and even though it's nominally for 85.5 shells, I can confirm it works perfectly fine in the 86.5 mm hubshell of this frame. With RED cranks, the fit is absolutely perfect with a 2.5mm driveside spacer and the preload adjuster turned all the way out. My subcompact chainrings sit a little closer to the frame than stock chainrings would, so with a 2 mm driveside spacer you could get some preload adjustment.