I noticed that the previous answer didn't give you the information you requested. So here is an update. In the last quarter of 2023, when you posed the question, the correct answer was Wonder of the Seas. She is a Royal Caribbean ship, the 5th Oasis class ship and weights in at 236,857 GT. She was launched in 2022 and measures 362 meters or 1188 ft long, 18 decks high and has 2867 guest cabins, for a double occupancy number of 5734. She is certified for a maximum 7084 passengers. Her crewsize is about 2300. Her guest services are broken up into 7 neighborhoods.
Royal Caribbean has held the title of largest cruise ship since 1999 when the Voyager of the Seas launched. Several ship in the line have held the title since then but the Oasis class sisterships have held the title from 2009.
Late in 2023, Royal Caribbean took delivery of the Icon of the Seas. She is larger than her Oasis class brethren at 250,800 GT, but obviously a derivative of her slightly smaller sisters. She is 1198 feet long and 20 decks high. 2805 cabins or 5610 passengers at double occupancy, but a maximum of 7600 passengers. Crew size is 2350. Note that although she is bigger, passengers have more room: passenger common space ratio of 44.7 compared to Wonders 41.3 ratio.
As far as I am aware she is the first ship to employ a large battery storage system as part of her power distribution system. She has 8 neighborhoods and boast so many other firsts that my hunt and peck typing style would be overtaxed. Her maiden voyage (with paying passengers) is next Saturday January 27th, 2024.
IT IS TIME FOR AN UPDATE: July 2025
Star of the Seas is about to launch. She will be the exact same size as the ICON and therefore tied for the largest ship. The following year or so Legend of the Seas will launch and there will be a three way tie for the largest ship (at least this is the announced plan). MSC has announced that they will build an even larger ship class, but this remains to be seen. The dynamics of the industry is changing and many European ports are closing access to MEGA Ships (and some to large ships).
Ports like Amsterdam are closing to Cruise Ships altogether. Pressure from residents to control the number of tourists and pollution concerns are the driving forces. Of course the wealth and increased value of the dwellings they currently enjoy because of their location may take a hit.
May you live in interesting times…..
(2023) Here is a side by side photo of the largest and 2nd largest cruise ships in the world (until they build another). Taken at Coco Cay, RCIs private island in the Bahamas.

