Elasticsearch's support for Java 9, alongside Java 8, marks a significant development for the Elastic Stack, reflecting a journey that began in 2015 to ensure compatibility and integration with Java's evolving features. The process involved substantial testing, including addressing a major performance regression identified during upgrades, which highlights the collaborative nature of open-source development. The introduction of multi-release JARs allows Elasticsearch to leverage Java 9-specific features while maintaining compatibility with Java 8, simplifying the development process for contributors. With Java's shift to a semi-annual release cycle, Elastic aims to rapidly adapt to new releases to enhance performance, although maintaining compatibility with long-term support (LTS) versions remains a priority. The company plans to keep users informed about future compatibility strategies, balancing innovation with stability in the Elastic Stack's development.