I'm seriously considering this frame for a new build but have not found any sizing guidance. I'm 5'11" (179.5 cm) tall 32" (81.25cm) inseem, what size would I order?

Thanks

Could you tell me the height of the saddle? 
I need about 79cm or 80cm
thanks

That's what I was told, but yes, 1800-1900 for the super light version seems to be a more realistic weight.

• 35mm Tire clearance This is conservative. I expected 4mm of clearance with 35mm tires. I have measured ~8mm of clearance with 33WAM tires and ~6mm of clearance with 37mm WAM tires
  
• Pretty standard road geometry--chain stays at 410mm are a little longer than I would like, but still plenty short Yes. It handles and climbs like a very good road bike. Very TCR like.
  
• Designed to mimic the Giant TCR in terms of stiffness numbers and feel (per the information listed on the website for the Permeants St-09 version)
• UDH
• T47i (85.5mm)
• Weight, they are claiming 760g frame and 325g fork including metal parts for a matte painted bare frame and like 20g more for a transparent green Time style paint. The seatpost weighs 98g and appears to use Ritchey-style hardware. This is likely >250g lighter than something like the SP cycle R088. EDIT: Given the weights posted here, S and M frames should be sub 800g with accessories and lighter-weight paint jobs. These weights have been verified and are realistic. The 680g marketing weight for the bare frame is also likely a very real number. Frame seems to match up well numbers wise with the Seka Spear RDC and the Elilee Blize XXE. Absolutely bonkers at this price.
  
• Claimed T1100, T1000, M65 blend. If true this is a nice high-end blend of medium-mod / high-strength and high-mod fibers
• Standard 1.5in headset Based on what we have seen so far, your best option is probably to buy a FSA No55R (40x51.8x8mm 36°/45°) headset separately and look for a FSA compatible stem / one-piece barstem
  

• Only one fork offset across the range, they should have a 50mm offset for the smallest 2 sizes IMO
• Stacks are a little high for a true race bike in the L, XL, and XXL.
• I personally think a few more MM BB drop would be nice, assuming a 30mm or 32mm tire size rather than 28mm will be run with this frame.
• Does not come with good rubber accessories. There are no rubber plugs to block the holes for unused mechanical cables for the FD or for the RD routing if wireless. The seatpost clamp cover looks like it was inspired by a napkin. See the notes below in the "Things to consider when ordering this frame" section for alternatives.
  

• Sizes S, M, L, XL, and XXL are now available to order and appear to be shipping to customers. This is an expansion of the range, as originally only S, M, and L sizes were offered. Alisa at LTK indicated that they needed to see demand before they expanded the offering, so it seems like we were successful.
• Speaking of Alisa, her contact is: longtengalisa@163.com. You can also contact her through the contact fork at LTbikes.com.
• You can also find a similar site Longtengbike.com, which leads you to Rex who is active on this forum.
• The frame is also available from Permants as the ST-09, Tideace as the CR266-D, and Haideli bikes as the CR266-D. Eddy from Haideli is also here on the forum.
• Per above, it seems like sourcing an FSA ACR No 55R LS headset is probably something you should do. FSA also sells the following headsets that are similar; FSA ACR No 55R STD (compatible but uses a different upper bearing, has slightly less internal space than the LS and cant quite do as tight of a hose bend as the LS), FSA no. 69 SRS (Compatible), FSA no 69/DUAL/56 SRS (not compatible, i think).
• LTK does sell an integrated barstem, but given current reviews, you are strongly advised to purchase a different bar. The LTK integrated barstem appears to use a proprietary spacer stack (poorly made and heavy). The barstem is also ~100g heavier than competitors in similar sizes, and there are doubts regarding the supplied bearing and C ring. Alternatives in this thread include the Tavelo Avro (@klrdd's build) and the XMCS one-piece (@BeeMC's build). The latter might be attractive because it does not require an adapter to interface with the FSA ACR headsets.
• My own build uses a two-piece bar and stem. The obvious choice here is the FSA SMR stem, but it is a bit heavy for a build like this. There are custom options available to integrate in lighter stems, incl. the Kalloy Uno, with this frame.
• Based on the contents of the thread so far, it seems prudent to order from LTK, the frameset + thru axles. This will come with one SL UDH hanger, an FD mount, both 7mm and 9mm saddle mount hardware, and an integrated seat post wedge.
• The standard clear appears to be tinted dark to hide some of the rough areas. On request it appears you can order a "clear clear" vs. the standard "black clear." Not sure what to make of this, but its likely informative to folks who want to get that "raw carbon" look.
• This frame does NOT include a Di2 battery mount. @Oker_s as a 3D printed solution and he as offered the .stl file to interested folks. I also believe the larger size Shimano one should work.
• An alternative seatpost clamp cover that fits aesthetically well is the one for the 2021 Giant Defy. Part No. 1724-SPSHIM-901. The cover looks great on the front, but it has additional overhang on the rear. Most people would consider this to be a significant upgrade over the original. Credit to @Oker_s for the find. A second alternative is to print one out of TPU. An STL file with my design is attached to this post.
• If you need to block up holes in the frame (e.g., the mechanical FD cable opening), I strongly recommend Tesa's Sugru. It's cheap, easy to mold into a plug that looks good, and removable with a pick or a set of tweezers.
• While some of the supplied accessories and rubber parts are low quality, the overall frame is high quality, and the few that are built have very impressed owners. Hopefully, more will be built and ridden, so we can see if this frame really belongs in the conversation for the best open-mold road frames available.