Scarpa revolutionised what was possible with a lightweight alpine touring boot when they released the F1 boots, which rapidly became the best selling model in this category. 
Weighing only 2.6 kg / pair (27 MP), the F1 is incredibly ergonomic, with a Boa closure system for the shell and two Velcro straps for the cuff. 
With an easy to use ski/walk system derived from the Alien race series and an amazing (at the time) 62° of friction-free cuff rotation, the F1 men's and women's boots supplied exactly the right combination of low weight, efficient walk mode and sufficient downhill control for modern lightweight "efficient" touring skis.

 

Skimo boot technology has developed rapidly the last few seasons with new materials and designs, and two years ago Scarpa upped the ante with an even lighter boot weighing in under 2 kg / pair, the F1 LT.
Scarpa shedded weight by removing the tongue completely and using a lighter Carbon Grilamid LFT polymer for the shell and cuff.
Cuff rotation was increased to 72° (47° backwards, 25° forwards) and one really does not notice the cuff at all when climbing.
To increase durability Scarpa moved the Boa cables, exposed on the F1, putting them out of harm's way inside under the gaiter that protects against snow entry. 
The new lighter construction was also stiffer, giving the F1 LT a 100 flex compared to the 90 of the F1s
The F1s had a pretty extreme ski mode, with 20-22° forward lean and for the F1 LTs this was reduced to 9-11-13°, with an additional 2° with the plastic spoiler added at the rear of the top of the liner.
Lighter, stiffer and even more efficient in climb mode, the F1 LT was an immediate success.

The F1 and F1 LT offer good downhill control but have a somewhat dry on/off character, lacking the progressive flex and power transfer of alpine boots. 
They also have only moderate compression around and over the foot with the Boa system.
It's easy to use, but not especially powerful when you want to really wrap the boots around your paws.
Skiers were asking Scarpa for boots that offer the climbing efficiency of the F1 LT with a more "alpine" downhill feel, boots with a more progressive forward flex.

For next winter Scarpa have produced two new boots, the F1 GT and F1 XT, which we were lucky to test this spring.
Both new models are developed from the F1 LT and both have a single shell buckle with Scarpa's Wave Lite closure system instead of the Boa system.
Let's take a look at look at how these compare to the F1 LT.

Shell
The F1 GT and F1 XT share the same shell mould as that of the F1 LT. All three boots have Scarpa's 3D Lamada Frame shell, with reinforced struts enveloping the heel and then progressing forward on each side to the front of the boot.
This design maximises shell stiffness while minimising weight, and provides a solid anchor for the base of the ski-walk mechanism, which is so important to the boot's performance since there is no tongue.
The F1 LT has four blanked-off holes protruding on the shell. It was always a mystery what these were for, and now we know -  these are the holes for the screws retaining the buckle that replaces the Boa system on the new boots.
Obviously these models have been in development for awhile....
The new models use a Grilamid Fiber Glass LFT composite for the shell which gives more progressive deformation during the turn than the Carbon Grilamid shell used for the F1 LT.
The F1 GT has a flex of 90 while the top of the range F1 XT has 110 flex.

Gaiter
While the F1 LT has a soft flexible gaiter that prevents snow entry into the shell and houses the Boa mechanism, the F1 GT & XT boots have a more sophisticated and robust gaiter.
Scarpa call the new gaiter Overlap Shield Tech and it combines Lycra with injected reinforced rubber-like flaps that provide excellent protection from the elements 
Overlapping flaps envelop the top of the forefoot, protecting the gaiter from the buckle mechanism and providing a uniform pressure from the buckle to the top of the foot without pressure points.

Shell Buckle
The F1 GT & XT share the same single shell buckle featuring Scarpa's Wave Lite closure system. A single cable passes across the top of the shell at the front, crosses the top of the forefoot where it connects to the buckle teeth
before connecting to a rivet on the instep. This design enables just one buckle with micrometric adjustment to provide effective closure around the foot with considerably more force than the Boa system could provide.
Closing the buckle tightly, the shell is more compressed and drawn closer to the foot than using the Boa system of the F1 LT.

Cuff
As well as sharing the same shell design as the F1 LT, both new models also share the same cuff design as the F1 LT, with a composite main collar and two overlapping front panels.
The cuff has an inverted "V" reinforced strut that rises on each side from the cuff rivet to the top of the ski walk mechanism.
Five struts on each side wrap around the cuff resulting in a stiff yet light supporting frame. Both new models have the same 72° cuff rotation as the F1 LT, allowing for a natural gait and extremely efficient skinning.
The cuff of the F1 GT is made using the same Grilamid Fiber Glass LFT composite used for the shell, while the cuff of the F1 XT is built with the stiffer Carbon Grilamid LFT used for the F1 LT.
Where the new boots differ from the F1 LT is in the design of the cuff front panels. While those of the F1 LT are just simple flat panels, for the  F1 GT & XT the outside panel has a reinforced central section that holds the teeth
of the cuff buckle. This thicker section is stiffer than the simple panels on the F1 LT, resulting in the cuff of the new models enveloping the calf more closely.
While these panels are riveted to the main cuff using the same rivets as those of the F1 LT, on the new boots the front panels extend higher up, providing a higher and more solid contact for the top strap on the new boots.

Cuff Closure
The F1 GT and F1 XT have more powerful cuff closure than the F1 LT.
The F1 LT has two Velcro straps for closure, a lower 35 mm strap with buckle closure and an upper 25 mm simple Velcro strap.
The new boots share the same single traditional metal buckle with micrometric adjustment positioned on the reinforced section of the cuff described above,. 
The F1 GT has a 45 mm Velcro Power Strap while the top of the range F1 XT has a 45 mm Booster Strap which supplies more progressive power transfer to the ski during the turn.

Ski / Walk Mechanism
All three boots use Scarpa's Speed Lock LT mechanism which was developed especially for the F1 series boots. 
The F1 LT & GT share the same black mechanism and have the same forward lean angle of 9-11-13°, while the silver coloured mechanism of the F1 XT has a slightly longer lower arm which pushes the cuff 
further forward to give forward lean of 11-13-15°. The spring retaining bar of the F1 XT is also lighter than that of the other models.
For next winter Scarpa will sell the F1 XT ski/walk mechanism as an accessory so that skiers can update their boots if they would like more forward lean.

Liners & Footbeds
All three models use Intuition Cross Fit Tour LT liners
Apart from the colour, we could not see any difference between the LT liners of the F1 LT and the LT2 liners of the F1 GT and XT.
The new boots have a new Ortholite footbed which offers a comfortable, breathable and more stable platform than the more basic footbed supplied with the F1 LTs.

Outsole
All three models use the Vibram UFO RS sole which covers the entire length of the boot.

So how do they ski?
Enough with the geeky details, what are they like to ski? Our testers usually tour with lightweight skimo boots (Arc'teryx, Scarpa F1, Scarpa F1 LT) so we were well placed to put the new boots through their paces.
It'll come as no surprise that the F1 GT & XT both climb as well as the F1 LTs. All three share the same 72° cuff rotation with friction-free movement, making these a veritable joy when climbing. 
The only difference is the weight, with the F1 LTs being the lightest (990 g) , followed by the XTs (1145 g) then the GTs (1165 g, all weights per boot 27 MP).
If weight and climbing efficiency are your priorites, then go for the F1 LT which is still the lightest.
Should your skimo route include some boot packing the three models are equally good, sharing as they do the full length Vibram UFO RS sole.
We found both new models offer superior downhill control thanks to the more powerful closure available with the buckle and the more progressive flex and power transfer through the turn. 
While the F1 LT supplies good control, power transfer to the ski has a rather "on/off" feeling (like many lightweight AT boots). The new boots with the reinforced cuff panels, buckles and higher performance
Velcro / Power Straps can transmit power more effectively to the ski and more progressively. 

The F1 GT is lighter than the F1 (1145 g compared to 1260 g per boot 27 MP), has 72° cuff rotation compared to the 62° of the F1, and offers superior downhill performance.
Although the GT's flex is slightly softer than that of the standard F1, the increased skiability supplied by the more progressive flex more than compensates and with a recommended price in France of 649 €, only 50 € more than the regular F1, the F1 GT is an interesting model that we're sure will please many tourers.

With a stiffer shell, cuff and beefier Power Strap, the top of the range F1 XT is the stiffest boot in the Tour Lite series, so if you're planning on using these with some of the wider "efficient" touring skis, or are looking for the highest downhill performance in a boot weighing only 1145 g, then the F1 XT is your boot.

Our thanks to David Hinchcliff and Franck Alary for testing these boots and to Scarpa France / Plein Nord.

SCARPA F1 LT, F1 GT & F1 XT SUMMARY TABLE

Scarpa F1 LT
Scarpa F1 GT Men
Scarpa F1 GT Woman
Scarpa F1 XT