As gravitational wave observatories discover more standard sirens, we
recognize that they can be an incisive probe of dark energy and gravity
in multimessenger combination with cosmic growth of structure.
Gravitational wave distance deviations from general relativity can be
related to growth deviations in many classes of gravity, providing deep
insight into cosmic physics. I also discuss how exciting new instrumentation
developments bring cosmic redshift drift closer to detection and measurement.