As predicted earlier this year in Mag-X, the RX L features a rear-end that's 110mm longer than standard.
The RX L measures a neat 5.0-metres long from head to tail, but there's no change to the standard car's 2790mm wheelbase.
Compared to the two-row RX, the L has a steeper tailgate to provide more space for passengers and luggage. The second row can be specified with two captain's seats or a 40/20/40 split-folding three-person bench.
The three-row RX will be available with two powertrains. The RX350L has a 216kW/357Nm 3.5-litre V6, an eight-speed automatic transmission, and the choice of front- or all-wheel drive.
Hybrid fans can opt for the RX450hL, which has a 3.5-litre V6 at its heart, a nickel-metal hydride battery, standard AWD and a total combined output of 230kW.
Standard features in the US include an 8.0-inch infotainment screen, radar-guided cruise control, lane keeping assistance, automatic high beam operation, three-zone climate control air-conditioning, leather seat covers for the first and second rows, 18-inch wheels, electric power steering, and a split-folding third row.
Available items include satellite navigation with a larger 12.3-inch screen, an 835W 15-speaker Mark Levinson sound system, blind spot monitoring, rear cross traffic braking, hands-free tailgate, and 20-inch alloy wheels.
The Lexus RX L goes on sale locally from February 2018, with specifications and pricing to be announced closer to the launch date.