Hi Spring fans, and happy holidays! I'm delighted to be joined again on this episode by my friend and fellow harbinger of doom (in the best possible way), Nate Schutta — co-author of the wonderful book Foundations of Software Engineering!

Happy holidays, everyone! The year may be winding down, but the Spring ecosystem continues unabated. We’re now a few weeks past the generational Spring Boot 4.0 release in November, and there have been tons of releases (and patches) since then. There’s also equal excitement reflected in posts from the community, so we’ve got a lot to dig into this week. So, without further ado…

• In last week’s installment of A Bootiful Podcast, I talked to the legendary Spring cofounder Juergen Hoeller
  https://spring.io/blog/2025/12/18/a-bootiful-podcast-juergen-hoeller
• Next-level Kotlin support in Spring Boot 4
  https://spring.io/blog/2025/12/18/next-level-kotlin-support-in-spring-boot-4
• Spring Shell 4.0.0-RC1 available now
  https://spring.io/blog/2025/12/19/spring-shell-4-0-0-rc1-released
• Spring Modulith 2.0.1, 1.4.6, and 1.3.12 released
  https://spring.io/blog/2025/12/20/spring-modulith-2-0-1-1-4-6-and-1-3-12-released
• Spring Tools 5 released
  …

When building AI agents with tool calling capabilities, developers often need insights into why an LLM chose a particular tool—not just which tool it selected. Understanding the model's reasoning process is important for debugging, observability, and building trustworthy AI systems.

Spring AI now (2.0.0-SNAPSHOT/1.1.3-SNAPSHOT) includes the Tool Argument Augmenter feature that enables dynamic augmentation of tool input schemas with additional arguments before sending tool definitions to the LLM. This allows AI applications to capture extra information from the model—such as reasoning, inner…

On behalf of the team, it is my pleasure to announce the release of the Spring Tools 5.0.1.

This release includes fixes for:

• log messages from language server appear in Error Log view in Eclipse #1747
• ai-related code lenses around Copilot do not show up in VSCode #1746
• TM Terminal superseded by Terminal Feature in Eclipse 2025-12 #1748

Detailed changes can be found in the release notes: https://github.com/spring-projects/spring-tools/releases/tag/5.0.1.RELEASE

To download the distribution for Eclipse and find links to the marketplace entries for Visual Studio Code, Cursor, and Theia, please…

Spring Modulith Christmas came early this year and I am happy to announce the release of Spring Modulith 2.0.1, 1.4.6, and 1.3.12. The releases contain the usual platform upgrades around Spring Boot and Framework. On top of that, we ship the following improvements and bug fixes:

• Allow resetting the shift in TimeMachine (2.0.1 – #1491)
• @ApplicationModuleTest does not bootstrap beans from test configuration (2.0.1 – #1495, 1.4.6 – #1494),
• CGLib proxy created for JdbcEventPublicationRepositoryV2causing issues in native image (2.0.1 – #1493)
• ClassNotFoundException for package-info from JavaPackage during runtime bootstrap (2.0.1 – #1487)
…

On behalf of the team and all contributors, I am pleased to announce that Spring Shell 4.0.0-RC1 is now available from Maven Central!

What's new?

This first release candidate comes with feature alignment with the previous generation as well as several improvements and bug fixes.

Major changes include:

• Support for debug mode
• Support for command completion and custom completion providers
• Support for hidden commands
• Support for command option validation with the Bean Validation API
• Support for exception mapping

For the complete list of changes, please check the release notes.

What's next?

Our plan for now is to make this release candidate as stable as possible in preparation for Spring Shell 4.0…

Following the announcement of the strategic partnership between JetBrains and Spring in May, I would like to share a global update on various Kotlin-related features and documentation enhancements we have made recently, with the goal of making Spring Boot 4 the best framework to develop backend applications with Kotlin.

Kotlin 2 baseline

Kotlin 2.0 introduced a new stable K2 compiler that compiles projects faster, performs smarter code analysis and allows the Kotlin team to evolve the language faster than with the K1 compiler. We recommend IntelliJ IDEA users to upgrade to 2025.3 to benefit…

On behalf of the team and everyone who has contributed, I'm happy to announce that Spring Boot 3.4.13 has been released and is now available from Maven Central.

This release includes 37 bug fixes, documentation improvements, and dependency upgrades. Thanks to all those who have contributed with issue reports and pull requests.

End of open source support for Spring Boot 3.4.x

Spring Boot 3.4.13 marks the end of open source support for Spring Boot 3.4.x. Please upgrade to Spring Boot 3.5.x or 4.0.x as soon as possible. If you are not yet ready to upgrade, commercial support for Spring Boot 3.4.x is available…