Seats 3888 according to the rules of the Kerbal Express Airlines.
This is a prototype and the final version may not be the same.
Despite the name, this is not a seaplane, please don’t land it in the water, it has plenty of fuel and redundancy to fly back to the KSC. The wings tanks can be optionally fueled at the cost of lower speed, altitude, and efficiency. The optimal altitude is where the nose is level and the plane flies straight at 2/3 throttle. For the standard loadout, this is 7000m @ 220m/s
A mod aircraft called Leviathan. Built with 334 of the finest parts, its root part is airbuscockpit.
Built in the SPH in KSP version 1.4.3.