Al Bawaba carried an explicit same-trip report identifying The Mercer Hotel as where Kylie Jenner was staying, while TMZ and Teen Vogue independently documented her leaving the exact property during the May 2018 Met Gala weekend.
Kylie Jenner stayed at The Mercer Hotel in New York during the May 2018 Met Gala weekend. A contemporaneous report carried by Al Bawaba described The Mercer as the hotel where she was staying, while Teen Vogue and TMZ independently placed her leaving the exact property during the same trip.
Source conclusion:
The cited sources support a stay at the named hotel.