  Observables related to the real part of the gravitational eikonal, such as
the deflection angle and time delay, have been found so far to have a smooth
post-Minkowskian (PM) expansion whose validity extends from the
non-relativistic to the most extreme ultra-relativistic (UR) regime, which
smoothly connects with massless particle collisions. To describe gravitational
radiation, the eikonal phase has to be promoted to a unitary operator for which
we motivate a proposal and start discussing properties in the soft-radiation
limit. A convergent PM expansion is found to only hold below an UR bound
(discussed in the GR literature in the seventies) above which a different
expansion is instead needed implying, in general, some non-analyticity in
Newton's constant. In this extreme UR regime soft radiative observables receive
contributions only from gravitons and are therefore universal. This generalises
the pattern discussed in \cite{DiVecchia:2020ymx} beyond the elastic case.
