  We present a new gauge for asymptotically flat spacetime that can treat
future and past null infinities ($\mathscr{I}^{+}$ or $\mathscr{I}^{-}$)
democratically. Our gauge is complementary to Bondi and Ashtekar-Hansen gauges,
and is adapted to the $S$-matrix being the natural observable. One new feature
is that the holographic directions are null. We present a set of consistent
fall-offs in terms of null coordinates at $\mathscr{I}^{+}$ and
$\mathscr{I}^{-}$, with finite BMS$^{\pm}$ charges. The diagonal BMS$^0$
symmetry of the gravitational $S$-matrix emerges upon demanding {\em
asymptotic} CPT invariance. Trivial diffeomorphisms, (absence of) log
fall-offs, possible enhancements of BMS algebra, and the possibility of
holographic renormalization of data at $\mathscr{I}^{+}_-$ and
$\mathscr{I}^{-}_+$, play interesting roles. Gory details of the various new
technical features that emerge, are elaborated in a companion paper to this
letter.
