This is an early developer milestone update of Couchbase Server 4.x series, which builds on top of Couchbase Server 4.0 by adding new enhancements such as optimized query execution with prepared statements and improved latencies with covering indexes. The release also introduces full SQL syntax for data manipulation with N1QL, allowing developers to easily bulk update documents through N1QL. Additionally, the developer preview is certified to run on Windows 10 and OS X El Capitan platforms, addresses several important bugs, and provides step-by-step guidance and resources for getting started with Couchbase Server 4.1 DP. However, it's still under active development and not intended for production deployments.