Which is better and why: upgrading directly from Spring Boot 2 to Spring Boot 4, or upgrading incrementally through Spring Boot 3?

An incremental upgrade - Boot 2 to Boot 3, then Boot 3 to Boot 4 - is almost always the safer choice for anything beyond a small application, even though it takes two migration cycles instead of one.

Going step by step means each hop only has to absorb one generation's worth of breaking changes (the javax.* to jakarta.* package rename in the Boot 2-to-3 move, then the Jakarta EE 11 and RestTemplate-deprecation changes in the Boot 3-to-4 move), and each intermediate version's compiler warnings and migration guides tell you exactly what broke and why. Jumping straight from Boot 2 to Boot 4 means absorbing both sets of breaking changes at once, with a much larger, harder-to-bisect diff - a failing test after the jump could stem from either generation's changes, and rollback becomes an all-or-nothing decision.

A direct jump can make sense for a genuinely small, low-risk service where the team is confident about the full change surface, but for most production codebases the incremental path trades a bit more calendar time for dramatically lower migration risk.