In this talk we present a prototype solution for multitenant, scale-out Prometheus. Don't worry, its open source! Our solution turns a lot of the Prometheus architectural assumptions on its head, by marrying a scale-out PromQL query engine with a storage layer based on DynamoDB & S3. We have disaggregated the Prometheus binary into a microservices-style architecture, with separate services for distribution, ingest and storage. By designing all these services as fungible replicas, this solution can be scaled out with ease and failure of any individual replica can be dealt with gracefully. This multitenant, scale-out Prometheus service forms a core component of the Weave Cloud, a hosted management, monitoring and visualisation platform for microservice & containerised applications. This platform is built from 100% open source components, and we're working with the Prometheus community to contribute all the changes we've made back to Prometheus.