Past half an acre, coverage rating and battery logistics decide everything.
Big lawns expose the difference between a toy and a tool. Look at rated coverage with margin to spare (a mower run at 100% of its rating finishes late and cuts unevenly), and prefer wire-free RTK on open ground so you're not burying hundreds of feet of perimeter wire.
Covers up to 2.5 acres on a single wire-free, AWD platform with up to 10 zones. The pick when the lawn is simply too big for everything else.
All-wheel-drive, vision-assisted, wire-free, and rated for very steep ground up to ~1.5 acres. The do-it-all premium pick for big, sloped, open yards.
A modular robot: the same wire-free base also takes snow-blower and leaf-blower attachments. Pricey once you add modules, but it earns its keep year-round.
The slope-to-price champion: genuine AWD, wire-free, and steep-rated for around a quarter the cost of Husqvarna's AWD flagship. Best value in the steep-and-large bracket.
Full one-acre coverage with no perimeter wire, and a camera that helps it see boundaries and obstacles. The value pick if you want wire-free at scale.
All-wheel-drive flagship that climbs slopes most robots can't touch. Expensive and wire-guided, but the answer for genuinely rough, steep terrain from a name pros trust.