TW was funded in part by European Research Council grant 320360 and by European Commission grant 730980. SvV was supported by the James Arthur Postdoctoral Fellowship. This research was partially supported by the Australian Gov- ernment through the Australian Research Council's Discovery Projects funding scheme (project DP200102471). Raw optical/UV/X-ray observations are available in the NASA/Swift archive (http://heasarc.nasa.gov/docs/ swift/archive, Target Names: AT2018fyk, ASASSN-18UL); the XMM-Newton Science Archive (http:// nxsa.esac.esa.int, obsIDs: 0831790201, 0853980201, 0854591401); and the Chandra data archive (https: //cxc.harvard.edu/cda/, obsID: 23289). NICER data is publicly available through the HEASARC: https:// heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/w3browse.pl.

This deposit contains the data related to Figures 2, 3, 4, 6, 7 and 11 in the accepted version of the manuscript "Rapid accretion state transitions following the tidal disruption event AT2018fyk" submitted to the Astrophysical Journal. It includes complimentary files.