Why Spring Boot 4.0 Is the Biggest Upgrade Since Spring Boot 2: Java 25, Modular Design & Native Speed

Gaddam.Naveen

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1. Spring Boot 4.0 vs Spring Boot 3.x — what actually changed?

Big picture:

• Boot 3.x was the “Jakarta + Native Image” generation (Java 17 baseline, first AOT/native support).
• Boot 4.0 + Spring Framework 7 is a refinement:
• Full modularization of Boot itself.
• First-class Java 25 support (min JDK 17, but tuned for 25).
• Built-in API versioning, instead of your own hacks.
• Declarative HTTP Service Clients (Feing-like, but “Spring-native”).
• JSpecify null safety annotations across Spring libraries.
• Better AOT / GraalVM native images (smaller, faster, more stable).
• Jackson 3, testing improvements, observability upgrades, etc.

Modularization change (huge difference vs 3.x):

• Boot 3.x had one big spring-boot-autoconfigure JAR with a ton of auto-configs you might never use.
• Boot 4 splits this into many smaller modules and more fine-grained starters, so you…