Spring Framework is introducing support for Jackson 3, the latest version of the popular JVM JSON library, in Spring Boot 4 and related projects. This significant update follows the Jackson 3.0.0 GA release and builds upon past Jackson integration improvements. The Spring and Jackson teams collaborated closely during the Jackson 3 release candidate phase, leading to several refinements. These include allowing co-existence of Jackson 2 and 3, a JDK 17 baseline, aligned defaults for JSON views, and enhanced null-safety and non-blocking parser capabilities. Spring Boot 4 will provide dependency management for both Jackson versions but will auto-configure only for Jackson 3, making it the default. Migrating applications are encouraged to adopt Jackson 3, although temporary use of Jackson 2 is possible with some manual configuration. Key migration steps involve updating package names from com.fasterxml.jackson to tools.jackson and adapting to new default settings in Jackson 3, such as alphabetical property sorting and date serialization formats. The introduction of an immutable JsonMapper in Jackson 3 replaces the mutable ObjectMapper from Jackson 2, simplifying configuration with JsonMapper.Builder. The deprecated MappingJackson2HttpMessageConverter is replaced by a more capable JacksonJsonHttpMessageConverter that uses serialization hints directly, eliminating the need for wrappers like MappingJacksonValue. Spring Security 7.0 will also support Jackson 3, enhancing safety by disabling default global typing and introducing a PolymorphicTypeValidator. Spring Data 4.0 brings full Jackson 3 support across its modules, though some, like Spring Data REST and Spring HATEOAS, will require a full migration to Jackson 3.