Still Gate Gourmet as of yesterday...since every station is negotiated more-or-less individually (sometimes in clusters/small groups but, AFAIK, never systemwide) it may happen eventually but I wouldn't anticipate it happening any time in the near future.

Hypothetically speaking, if UA were to change caterers at a major hub -- like IAD -- given the proportion of the airport's overall catering business that represents I would expect the outgoing caterer to impact more than 50 jobs and trigger the requirement for a WARN notice at least 60 days before taking effect [baring things like unforeseeable events/acts of God/force majeure where they may be filed retrospectively). Per the Virginia Department of Workforce Development and Advancement -- https://www.virginiaworks.gov/warn-notices/ -- the last time Gate Gourmet filed a WARN notice (affecting 330 employees) was back in 2020... For reasons I'm sure surprise no one.