Grafana Labs has transitioned from contributing to Cortex to launching Grafana Mimir, an open-source long-term storage solution for Prometheus that supports massive scalability. Cortex, historically used for distributed storage, offers horizontal scalability and high availability for Prometheus, but its architecture can lead to operational complexities. To address these challenges, a new storage engine for Cortex was developed, based on Prometheus TSDB and Thanos core components, eliminating the need for an index store while maintaining scalability and performance. This new blocks storage architecture, though still experimental, is being tested at scale and shows promising results in reducing complexity compared to the traditional chunks storage. The development involved significant collaboration within the community and between Cortex and Thanos projects, highlighting an ongoing effort to improve the efficiency and reliability of Prometheus storage solutions.