In the past, if you needed a mountaineering boot with a removable liner (for drying out in your sleeping bag on overnight adventures), your only choice was big, heavy, double boots. No longer is that the case. The Arc'teryx Acrux AR have a removable liner but are as nimble as any super-gaiter boot. These boots kept our feet warm and dry on multi-night winter trips at altitudes above 14,000 feet (4200m). Our testers liked the velcro ankle strap which helped quickly dial in the fit of the boot for different applications.
Some of our testers found the sole to be slightly flexible on steep ground. These are one of the most expensive boots in our review, but we think they could be an excellent tool for climbers spending multiple nights out in cold environments.