Over the last several years, it has been shown that black hole microstate
level statistics in various models of 2D gravity are encoded in wormhole
amplitudes. These statistics quantitatively agree with predictions of random
matrix theory for chaotic quantum systems; this behavior is realized since the
2D theories in question are dual to matrix models. But what about black hole
microstate statistics for Einstein gravity in 3D and higher spacetime
dimensions, and ultimately in non-perturbative string theory? We will discuss
progress in these directions. In 3D, we compute a wormhole amplitude that
encodes the energy level statistics of BTZ black holes. In 4D and higher, we
find analogous wormholes which appear to encode the level statistics of small
black holes just above threshold. Finally, we study analogous Euclidean
wormholes in the low-energy limit of type IIB string theory; we provide
evidence that they encode the level statistics of small black holes just above
threshold in AdS5 x S5. Remarkably, these wormholes appear to be stable in
appropriate regimes, and dominate over brane-anti-brane nucleation processes
in the computation of black hole microstate statistics.