Java 25 is the LTS that most production teams have been waiting for since Java 21. After spending several weeks working through a real Spring Boot 3.4 codebase with a Java 25 migration — updating dependencies, testing each JEP feature against actual production code, and specifically trying to break things with the new patterns — I came away with a clearer picture of which JEPs matter day-to-day versus which ones are mostly interesting in theory. What I did not expect: JEP 491 (synchronized no-pinning) had the biggest practical impact, and I found it in places I wasn’t looking. A legacy JDBC connection pool that I assumed was fine under virtual threads turned out to have been quietly starving the carrier pool. The other surprise was how little JEP 495 (Simple Source Files) moved the needle in a production context — useful for scripts and documentation, but rarely relevant inside a mature codebase. This post takes the format I could not find anywhere: one JEP per section, each with a concrete before-and-after, an explanation of what the JVM actually does differently, the pitfall that will bite you, and a copy-paste AI prompt to retrofit your existing codebase. The Java 21 to 25 feature overview and the upgrade AI prompts playbook are good starting points before this deeper dive.