  We present vertex operators for ambitwistor strings around generic
Yang-Mills, gravity and NS-NS backgrounds. The requirement that vertex
operators lie in the BRST cohomology of the worldsheet theory enforces the
appropriate linear equations of motion (as well as gauge fixing conditions) for
the respective perturbations in these backgrounds. Due to the nature of
ambitwistor strings, no approximation is taken and all calculations around the
backgrounds are exact.
