  Fermi Large Area Telescope (LAT) has recently detected 8 gamma-ray
millisecond pulsars (MSPs), providing an unprecedented opportunity to probe the
magnetospheres of these low-spin-down pulsars. We performed 3D emission
modeling, including various Special Relativistic effects, in the context of
pair-starved polar cap (PSPC), slot gap (SG), and outer gap (OG) pulsar models.
Most of the light curves are best fit by SG and OG models, surprisingly
indicating the presence of narrow accelerating gaps limited by robust pair
production. All model fits imply high-altitude emission, and we observe
exclusive differentiation of the current gamma-ray MSP population into two
sub-classes: light curve shapes and lags across wavebands impose either PSPC or
SG / OG-type geometries.
