Couchbase Server 4.0 Release Candidate introduces significant architectural advancements and new capabilities, highlighted by the N1QL Query Language, which combines SQL's simplicity with JSON's flexibility for scalable application development. The release includes Global Secondary Indexing (GSI) to enhance the speed of document access and Multi-Dimensional Scaling (MDS) for optimized hardware resource allocation. It also features the advanced storage engine ForestDB, designed for SSD efficiency, and simplified security compliance with native LDAP integration and auditing capabilities. Additionally, powerful global data distribution is achieved through Cross Datacenter Replication Filtering, which allows data to be filtered and distributed with low latency across geographical locations. While this release candidate is not yet production-ready, Couchbase encourages feedback to refine the final product, offering comprehensive resources and support for developers to explore the new features.