Singapore Airlines is planning to add a four-seat first class to the Airbus aircraft it uses for its longest routes, a bet to attract high-spending travelers to flights that can top 17 hours.

The carrier will add the new seats to seven Airbus A350-900 URLs, or ultra-long-range aircraft that it uses for lengthy trips, including its longest, between New York and Singapore. It will also revamp its cabins on long-haul Airbus planes with new business-class seats that will likely include a suite with a sliding door, a popular design carriers are increasingly adopting to sell privacy as an onboard perk.

Singapore said the fresh first- and business-class seats will have new in-flight entertainment but the carrier didn’t disclose many details about the new cabins. CEO Goh Choon Phong said in a news release that they will “push the boundaries of comfort, luxury, and modernity.”

Airlines have been investing billions of dollars to revamp their premium cabins to chase travelers willing to shell out for more space on board. They range from international airlines like Singapore’s jumbo jets to smaller carriers like JetBlue Airways that fly smaller Airbus airplanes, both of which feature suites with sliding doors

Singapore’s retrofit plans also include new cabins for 34 long-range Airbus A350s, part of a 1.1 billion Singapore dollar (about $835 million), overhaul it plans to start putting into service in mid-2026. Those will still have 42 business-class seats, 24 premium economy seats and 192 in standard economy, up from the 187 economy seats it currently lists as the aircraft’s configuration.

The ultra-long-range airplanes now have only business class and premium economy cabins. After the new cabin design with first class is installed, total business-class seats will go up to 70 from 67 and the airline will offer 58 premium economy seats, from the 94 it currently offers, according to the carrier’s website.

Most U.S. carriers have already done away with long-haul first-class cabins, or are in the process of doing so, in favor of larger business class.

American Airlines is retrofitting some of its Boeing 777s to include a 70-seat business class instead of separate first- and business-class cabins, and will upgrade its business-class seats on 777s and Boeing 787 Dreamliners to designs that include sliding doors. Supply chain issues have slowed some retrofits amid demand for premium-seats post-pandemic throughout the industry.

Some carriers, however, plan to keep first class, at least on some routes. German carrier Lufthansa’s new first class “suites” will debut Nov. 9.