  High energy X-ray and ultraviolet (UV) radiation from young stars impacts
planetary atmospheric chemistry and mass loss. The active $\sim 22$ Myr M dwarf
AU Mic hosts two exoplanets orbiting interior to its debris disk. Therefore,
this system provides a unique opportunity to quantify the effects of stellar
XUV irradiation on planetary atmospheres as a function of both age and orbital
separation. In this paper we present over 5 hours of Far-UV (FUV) observations
of AU Mic taken with the Cosmic Origins Spectrograph (COS; 1070-1360 Angstrom)
on the Hubble Space Telescope (HST). We provide an itemization of $120$
emission features in the HST/COS FUV spectrum and quantify the flux
contributions from formation temperatures ranging from $10^4-10^7$ K. We detect
13flares in the FUV white-light curve with energies ranging from $10^{29} -
10^{31}$ ergs. The majority of the energy in each of these flares is released
from the transition region between the chromosphere and the corona. There is a
100$\times$ increase in flux at continuum wavelengths $\lambda < 1100$ Angstrom
in each flare which may be caused by thermal Bremsstrahlung emission. We
calculate that the baseline atmospheric mass-loss rate for AU Mic b is $\sim
10^8$ g s$^{-1}$, although this rate can be as high as $\sim 10^{14}$ g
s$^{-1}$ during flares with $L_\textrm{flare} \simeq 10^{33}$ erg s$^{-1}$.
Finally, we model the transmission spectra for AU Mic b and c with a new
panchromatic spectrum of AU Mic c and motivate future JWST observations of
these planets.
