Custom Zpacks Arc Slim backpack
Weighs 493 grams / 17.4 oz on my scale

21″ Torso length
Cuben fiber with carbon stays and a tensioned mesh backpanel
Roll top closure with velcro/buckles
Reinforced bottom panel
2 side pockets, 2 hip belt pockets
Waistbelt is relatively short – will likely fit up to about a 36″ waist or so.
This pack was custom made to be as light as possible for speed hiking/fastpacking on the JMT and was only used for a few short trips, likely about 10 nights all together. Selling for a friend. It is in good to excellent used condition with some minor wear in spots but no holes or major damage that I can find.
See photos for the spec sheet.

Note: the pack is missing the 1″ male end of the plastic buckle on the waistbelt, and the small 1/2″ male end of the plastic buckle on the top strap that goes over the roll-top closure to cinch it down – this one is not really necessary and the pack will work just fine without it. It should be fairly easy to replace these.

It looks like the closest thing Zpacks currently makes is the 40L Arc Haul which goes for $399 and is a bit heavier.