We present continued multi-frequency radio observations of the relativistic tidal disruption event Swift J164449.3+573451 extending to t approximate 600 days. The data were obtained with the JVLA and AMI Large Array as part of our on-going study of the jet energetics and the density structure of the parsec-scale environment around the disrupting super-massive black hole. We combine these data with public Swift/XRT and Chandra X-ray observations over the same time-frame to show that the jet has undergone a dramatic transition starting at approximate 500 days, with a sharp decline in the X-ray flux by about a factor of 170 on a timescale of delta t/t < or = 0.2. On the other hand, our radio data uniquely demonstrate that the low X-ray flux measured by Chandra at approximate 610 days is consistent with emission from the forward shock. Projecting forward, we predict that the emission in the radio and X-ray bands will evolve in tandem with similar decline rates.