Spring Boot 4.0 is released recently (on November 20, 2025), represents a significant evolution built on Spring Framework 7, emphasizing modularity, efficiency, and alignment with recent Java and Jakarta EE standards.

Here we intend to explore whether teams should upgrade to this new version, what are the benefits of doing so and also give pointers on how this can be done.

You should consider upgrading if your project can benefit from modern Java features, improved performance, and better maintainability - especially if you're building new features or planning long-term support. However, if your application is stable, in maintenance mode, or relies on legacy dependencies still tied to Java 11/17 without immediate needs for new capabilities, you might delay until you've tested in a staging environment. Upgrading now ensures access to security patches and ecosystem support for the next several years.

Key Benefits of Upgrading

Spring Boot 4.0 introduces targeted enhancements that make applications leaner, faster, and more robust. Here's a breakdown of the major benefits:

Benefit	Description	Why It Matters
Modular Codebase and Smaller JARs	Complete modularization splits the framework into focused auto-configuration modules and dedicated starters (e.g., one per technology like JMS or REST), replacing monolithic "fat starters." Classic starter POMs are provided for backward compatibility.	Reduces application footprint and memory usage (up to 20-30% smaller JARs in some cases), improves startup times, and enhances clarity for large-scale micro-services. Ideal for cloud-native deployments.
Java 25 First-Class Support	Minimum JDK 17 (LTS), with full compatibility and optimizations for Java 25, including virtual threads, pattern matching, records, and sealed classes.	Unlocks JVM performance gains like better garbage collection and concurrency, making apps more scalable and efficient without manual tweaks.
Enhanced Null Safety	Portfolio-wide adoption of JSpecify for annotations, integrated with tools like IntelliJ IDEA and Kotlin 2.2+.	Catches null-related bugs earlier, reducing runtime errors and improving code reliability-especially valuable for Kotlin users with smoother coroutine support.
Improved Observability and Metrics	Deeper Micrometer 2.x integration with OpenTelemetry, plus better tracing and metrics out-of-the-box.	Simplifies monitoring in distributed systems, helping with debugging and performance tuning in production.
REST and API Modernization	Built-in support for HTTP Service Clients (annotate interfaces for auto-implemented clients) and API versioning in REST apps.	Speeds up development of microservices with less boilerplate, while enabling easier evolution of APIs without breaking changes.
Security and Maintenance	Alignment with Jakarta EE 11 (Servlet 6.1, JPA 3.2, etc.), removal of deprecated APIs, and upgraded dependencies (e.g., Jackson 3, Hibernate updates).	Stronger security posture against vulnerabilities, lower long-term support costs, and easier integration with modern tools like Gradle 9.
Build and Deployment Efficiency	Faster Docker-native builds, improved Buildpacks, and better AOT/GraalVM native image support.	Accelerates CI/CD pipelines and reduces deployment times, particularly for containerized environments.

These changes build on Spring Boot 3.5's foundations, focusing on developer productivity and runtime efficiency rather than breaking overhauls.

How to Upgrade : Step-by-Step Guide

The official migration is straightforward for most projects, thanks to Spring Boot's design. It's recommended to first ensure you're on the latest 3.5.x patch release. The process typically takes 1-2 days for a mid-sized app, but use automation tools for larger codebases. Follow the official Spring Boot 4.0 Migration Guide for full details.

1. Prepare Your Environment:
   • Verify your JDK is 17+ (21 or 25 recommended). Update if needed.
   • Upgrade to Spring Boot 3.5.x first: In your pom.xml (Maven) or build.gradle (Gradle), set <spring-boot.version>3.5.0</spring-boot.version> (or latest patch) and run a full build/test cycle.
   • Review dependencies: Use mvn dependency:tree or ./gradlew dependencies to spot outdated libs (e.g., Jackson, Hibernate). Spring Boot 4.0 manages most upgrades automatically.
2. Update Build Configuration:
   • Maven: Change the parent version:
     • Switch to modular starters if desired (e.g., replace spring-boot-starter-web with spring-boot-starter-web-core + specifics like spring-boot-starter-json), but stick with "classic starters" for minimal changes.
   • Gradle: Update the plugin:
     • Ensure Gradle 8.14+ (9 supported).
3. Handle Breaking Changes:
   • Add the properties migrator for auto-handling renamed/removed configs:
     • Run your app; it will log warnings for issues (e.g., Jackson 2-to-3 defaults via spring.jackson.use-jackson2-defaults=true).
   • Scan for deprecations: Update any 3.x-deprecated APIs (e.g., in security or data modules). Tools like OpenRewrite can automate this.
   • Test serialization (JSON/XML) and database interactions, as Hibernate/JPA upgrades may affect queries.
4. Test Thoroughly:
   • Run unit/integration tests. Focus on REST endpoints, security, and actuators.
   • For Kotlin projects: Ensure 2.2+ and test coroutines.
   • Use Spring Boot's Actuator for diagnostics during startup.
5. Automate for Ease (Especially Large Projects):
   • OpenRewrite/Moderne: Free recipe-based tool for automated refactors (e.g., dependency updates, API migrations). Run via CLI: rewrite run --recipe org.openrewrite.java.spring.boot4.UpgradeSpringBoot_4_0.
   • IntelliJ IDEA or VS Code: Built-in Spring Boot tools highlight changes and suggest fixes.
   • If multi-module: Upgrade incrementally (one module at a time) to isolate issues.

Post-upgrade, monitor for performance gains (e.g., via Micrometer) and contribute feedback to the Spring community if you hit snags. If your app uses custom starters, refactor them to align with modularization. Overall, the upgrade path is smoother than past majors like 3.0, prioritizing compatibility. If you encounter specific errors, share your build file for more tailored advice!