Abstract: At Zillow, we calculate a Zestimate® home value for about 100 million homes nationwide daily. But between batch runs, users could update their home facts or even list their home on the market. Housing markets move fast, and we want Zestimates to reflect the latest state of our housing data. In this talk, I will present the architecture of the Zestimate and the infrastructure powering it. Inspired by Lambda Architecture, the Zestimate relies on both a near real-time and a batch component. I will highlight how the design allows us to be nimble in the face of data changes, while not sacrificing algorithmic accuracy during daily batch runs.