I might just set it up 44T, and maybe get a 48T aero on demand for specific occasions. This is the confusing message from Enve:
I just spoke with SRAM and here’s what they told me. Essentially their calculator is designed for mountain bikes only. So at this point if your bike is not listed the shortest chainstay you can put in is a 435mm. The MOG has a 420mm. Their biggest ring is also a 38T an not a 42T. You can find that calc here: SRAM | AXS Essentially what the SRAM tech recommended to me was to use the A position as that is the default rear der position for shorter travel mtb, and being a gravel frame that should make sense here. In terms of the chain length, you’ll just need to manually use the old technique of big ring to big ring, add two links without running it through the derailleur to determine chain length. That was SRAM’s recommendation as he told me they haven’t really tested this yet on gravel bikes. However he hasn’t heard of any news of this not working and I can back that up too. We’ve had a couple customers set this up and I haven’t heard of any issues, but that’s only a couple here and there of course.Sorry this is a bit of a gray area but it’s all very new with what SRAM launched here and because it’s technically a mtb drivetrain it seems like they didn’t look super closely at Gravel bike compatibility from what they told me.
That’s a surprising comment given how many folks are using AXS “MTB” drivetrains on gravel bikes these days (including some OEM bikes coming with this groupset). It’s got to be one of the most common drivetrains for gravel at this point (at least at the pointy end). I believe Keegan was running a 48 or 50t chainring with the new AXS transmission at unbound (and I don’t think anyone is choosing a 38 chainring to race gravel), so there certainly isn’t a 38t chainring limit.
Definitely some kind of professionally installed and semi-permanent full frame film like invisiframe or ridewrap if you’re settled on a carbon frame.
I arrived at a similar gravel race and gravel adventure bike conclusion a few years ago. Kept my carbon gravel bike as the racer and and had a custom titanium frame made for adventure. Biggest factor in choosing titanium was abuse and abrasion, but sounds like you’ve got enough budget to buy carbon and then protect it adequately (and replace it in a few years if needed). My Ti is ~1kg heavier than my carbon but I reckon it could be as little as ~500g if I’d used a more boutiquey high-end Ti company and more lightweight forks (mine are carbon but also weight rated to take a front pannier rack if I want). For bikepacking etc. I find that an acceptable weight penalty but you might not.
It was also important to me to think about drivetrain cross-compatibility between the two bikes. I know you’re waiting for 12s GRX so this might not be an option for you. Both of my gravel bikes are GRX810 2x which means I can swap wheels without cassette changes. Also means I can take wheels from the road bike (and my Ti bike can double as my winter road bike)
For an upcoming long and hilly bikepacking race I’m going to fit the GRX600 chainrings to my 810 chainset on the Ti bike which brings me from 48/31 to 46/30. I’m also going to stick an 11-40 cassette in which is meant to be seamless even though Shimano don’t say so. So bigger gear range is possible.
I’m also in the process of upgrading handlebars on the Ti bike and discovering my choices are limited by the fact that I want to be able to fit traditional clip-on aerobars with pretty tall risers. Aerobars may be getting banned rapidly in all the gravel races where you’d use your Kaius/Ostro, but you’re definitely going to want them on an adventure bike if you ever intend to compete on it.
Overbuilt carbon forks I mentioned earlier are Rodeo Spork - makes me wonder if the latest version of the bike they were designed for could be of interest to you. I’ve never looked at it in much depth but it seems very full-featured. Rodeo TrailDonkey 4.0
As a counterpoint, I’ve since gone to R8100 on my road bike so it’s now 12s and cassette swaps are back on the table a bit more often. It’s less of a pain than I expected. Main time saver is that I’ve shimmed all my brake rotors so the calipers never need adjusting.
Swapping freehub from Shimano to XDR might be a bigger task depending on the hubs you choose.
3 of my hubsets are all DT Swiss EXP with 36t ratchets so I could in theory just pull whole freehub assemblies off comlete with cassettes and swap them around without tools. I’ve done it once in a rush before a race but have otherwise avoided doing so in case the process ends up getting grit/dirt in the ratchet grease. Assuming I’m being unnecessarily cautious then actually this might be the most versatile and user-friendly method out there!