  SmB$_6$ exhibits a small (15-20 meV) bandgap at low temperatures due to
hybridized $d$ and $f$ electrons, a tiny (3 meV) transport activation energy
$(E_{A})$ above 4 K, and surface states accessible to transport below 2 K. We
study its magnetoresistance in 60-T pulsed fields between 1.5 K and 4 K. The
response of the nearly $T$-independent surface states (which show no
Shubnikov-de Haas oscillations) is distinct from that of the activated bulk.
$E_{A}$ shrinks by 50% under fields up to 60 T. Data up to 93 T suggest that
this trend continues beyond 100 T, in contrast with previous explanations. It
rules out emerging theories to explain observed exotic magnetic quantum
oscillations.
