  Extremely irradiated hot Jupiters, exoplanets reaching dayside temperatures
${>}$2000 K, stretch our understanding of planetary atmospheres and the models
we use to interpret observations. While these objects are planets in every
other sense, their atmospheres reach temperatures at low pressures comparable
only to stellar atmospheres. In order to understand our \textit{a priori}
theoretical expectations for the nature of these objects, we self-consistently
model a number of extreme hot Jupiter scenarios with the PHOENIX model
atmosphere code. PHOENIX is well-tested on objects from cool brown dwarfs to
expanding supernovae shells and its expansive opacity database from the UV to
far-IR make PHOENIX well-suited for understanding extremely irradiated hot
Jupiters. We find several fundamental differences between hot Jupiters at
temperatures ${>}$2500 K and their cooler counterparts. First, absorption by
atomic metals like Fe and Mg, molecules including SiO and metal hydrides, and
continuous opacity sources like H$^-$ all combined with the short-wavelength
output of early-type host stars result in strong thermal inversions, without
the need for TiO or VO. Second, many molecular species, including H$_2$O, TiO,
and VO are thermally dissociated at pressures probed by eclipse observations,
biasing retrieval algorithms that assume uniform vertical abundances. We
discuss other interesting properties of these objects, as well as future
prospects and predictions for observing and characterizing this unique class of
astrophysical object, including the first self-consistent model of the hottest
known jovian planet, KELT-9b.
