I had breast cancer in 2017 and was told that because of the danger of lymphedema (a complication of having lymph nodes removed to check for cancer) I probably shouldn't carry an overnight-sized backpack again. Despite this danger, I have made the choice to continue to backpack. However, with shoulder straps it has not been very comfortable because of the amount of scar tissue I have in my underarm area. As a result, I have chosen to use very well padded backpacks, even though they are relatively heavy. When I saw the vest option for the Swift X I thought it might help with my issues, and indeed it has. I had a lumpectomy and am medium-chested (C-D cup size), so I don't know if the vest would work as well for people who had mastectomies or are who have larger breasts, but for me it's been amazing. There is no underarm rubbing at all because the vest doesn't go up to my underarm area. This means that the area where lymph nodes were removed has no additional pressure on it and I suspect this reduces my chances of developing lymphedema, although I don't know that for sure.
Three other things that I really appreciate about this backpack are: the transfer of weight to my core (I actually had sore upper abs after my latest Yosemite trip with a load that pushed the 35 pound limit); the ability to cinch the pack down to day-pack size for summit days; and the waist belt system which is great for my curvy hips. I've always preferred women's fits in backpacks but this uni-sex pack works great for my body.
All around, I couldn't be more pleased. This pack will be the one I use exclusively for all but the shortest day hikes.

Fixed Whitney's van at my shop and he turned me on to Six moons. Bought the swift x. Just did a 3 day 25 mile trek with 35 lbs. I own lots of packs. Best 1 I've ever had !!!!!!

Just got this pack in the coyote brown VX21, with the standard shoulder straps bc the vest wasn’t available to me. The pack is not exactly ULTRAlight but a typically sturdy and versatile lightweight SMD pack. If you know SMD, you know what to expect. One thing that did surprise me, though, is, compared to my SMD Fusion 65 (1st gen) this supposedly 40/45/49 liter pack is an absolute GIANT. I assumed the Swift would sit/fit in between my Fusion 65 and my 30’ish liter SMD DayBreaker (now Wy’East) but it’s definitely bigger than the Fusion. I’d be interested to learn how these sizes are measured (thought I knew but seeing these two next to each other has left me confused). That said, I’m not at all unhappy with the pack, just surprised with the size(ing).

Second thing I’ll say is there’s a lot of excess strapping. But I’ve actually put that to good use (I think) so instead of trimming it I’ve tinkered a bit: (1) I’ve redone the yellow paracord to run across the front pocket as well as sides, and (2) more importantly, and ingeniously if I do say so myself, I’ve run the shoulder straps through the extra attachment points otherwise reserved for the vest harness by running them diagonally across the back (through the hip belt attachment gap). This way the pack should sit closer to my back, like the vest (remains to be tested in the field but maybe try this hack if you, like me, wanted the vest but could only get hold of the standard yoke).

This pack was so comfortable. I bought with the standard type shoulder straps and they were fine. Hip pockets easy to negotiate and held quite a bit. 4 night, 3 day trip on the Three Capes trail at bottom of Tasmania (Australia). Did not have to carry tent nor sleeping mat but I know exactly where they'll fit for next trip.

This is my first dip into the vest harness style and I LOVE it. Haven't been able to get on an overnight quite yet, but some weighted day hikes have been so great! Love the vest harness, the side pockets, all of it. Thanks for making a rad pack!