Electro-optic modulators change the intensity of light in response to electric signals and have attracted much attention recently as they enable active photonics. Reaching gigahertz speeds is an important milestone that makes applications in remote sensing and communications accessible. Most demonstrations target either on-chip or fiber applications. Instead, modulators that operate on free-space light have long been very challenging to realize. Here, we show that a thin film metasurface from sub-wavelength Mie resonators enables highly efficient and ultra-compact modulation of light up...