Spring I/O 2026: Field Notes from Barcelona

Spring I/O 2026 wrapped in Barcelona on Wednesday. Three days at the Palau de Congressos. A thousand-plus developers, five tracks, sixty sessions (or there abouts) Here are the things I'm still thinking about..

Agents everywhere

It was a Spring AI conference with a Spring Boot conference attached.

That's not a complaint. Count the programme yourself. Across the two main days, roughly a third of the main-track sessions were about Spring AI, MCP, agents, or building on LLMs. Josh Long opened Day 2 at eleven with Bootiful Spring Boot 4. By twelve, the Auditorium had moved on to The Spring AI Ecosystem in 2026: From Foundations to Agents.

A few years ago the headline topics were reactive programming, observability, Kotlin adoption. This year the big rooms belonged to agents. Hallway conversations tracked the programme. Prompts, tool-calling, MCP clients, evaluation harnesses. The classic Java-platform conversations still happened. They were in smaller groups and later in the evening.

Rod Johnson on the road

Rod Johnson gave Building Killer AI Agents on Your Spring Stack with Embabel.

Four days earlier he gave essentially the same pitch to the London Java Community at Tessl. Same message, two cities, one week. When the person who shaped Java enterprise for two decades picks one topic and tours with it, it's worth noticing what that topic is.

Right now that topic is agents and AI, not Spring.

The sessions that didn't get the main stage

Migration content was on the programme if you went looking. Raquel Pau ran a session on Hybrid Modernization, pairing OpenRewrite's precision with LLMs. Moritz Halbritter gave Inside Spring Boot 4: Restructuring for the Future. Tim te Beek and Merlin Bögershausen ran a full workshop on Prepare Your Next Spring Boot Migration. Juergen Hoeller on Core Resilience Features in Spring Framework 7. All worth your time when Spring I/O put the videos up.

A few things from the HeroDevs corner

Two colleagues on the programme. Anthony Dahanne spoke on Paketo Buildpacks: the Spring Boot way to build images, and more! Marcin Grzejszczak followed with From Contracts to Confidence: Spring Cloud Contract 5 in the Age of AI. Watch both when the videos land.

Over at our booth, Wendy ran what I think is the best prize draw of the week: 3D-printed articulated dragons and dragon eggs. If you were at Spring I/O and walked past without picking one up, I'm sorry, but also: what were you doing.

The documentary

One other thing worth flagging. A Spring documentary I appear in released its trailer yesterday. You can watch it on YouTube. I'll say more about it when the full piece drops.

And since the topic is Spring anyway: if you want a five-minute reality check on where your team actually sits on the EOL calendar, we built a quiz and ran it at Spring I/O

15 questions about what changed between Spring 3.5 and 4.0
Turns out most Spring developers are just 'ok' on things like this. Well when I say most - it was about 100 devs @ Spring IO. Next week we're at JCON and Devoxx France so maybe the answers will be different.

What I'm taking home

The Spring ecosystem is in the middle of something bigger than a framework upgrade. The shift from "web framework" to "agent platform" is the story this year and it's going to keep getting louder through the rest of 2026. That's a genuinely interesting place to be standing, if you like being on ground that moves.

I'll write more once the videos are up and I've had time to rewatch the sessions I missed. Barcelona was full of good weather, friends, coffee, conversations, and dragons. What more do you want.

• Java
• Spring

Steve Poole

Author

HeroDevs