I believe that the 33L is frameless. Larger models do have a frame, though. You are right about the full hip belt and the general design, however -- my idea is that if we carry a 6+ kg load, this design is preferable to, say, a zPacks' Nero. But we are still very early in the "thinking about a trip before we plan" phase

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To give additional background -- we are talking about the North Kaibab trail (Grand Canyon). May 2018. The initial idea is to camp two nights at Bright Angel carrying enough food to avoid paying 22$ for a breakfast (!). But we haven't ruled out booking a dorm and shelling big bucks for a pittance. Would make for an easy walk with basically nothing but a couple of litres of water, a jacket and misc stuff.