Google Summer of Code 2026 With the Kotlin Foundation: Recap

Google Summer of Code 2026 has wrapped up! This was the Kotlin Foundation’s fourth year participating in GSoC, bringing new contributors into the Kotlin open-source ecosystem through hands-on projects and mentorship.

This year, two projects successfully reached completion, tackling two areas of the ecosystem: improving recursion support in the Kotlin/Wasm backend and building a global picture of where Kotlin is taught.

Congratulations to Ayako Hayasaka and Mark Seif Khalil, and a huge thank-you to our mentors for supporting them throughout the program!

Here’s more on what they accomplished.

Tail call support in the Kotlin/Wasm backend

Contributor: Ayako Hayasaka
Mentor: Charlie Zhang (JetBrains)

Ayako’s project added support for WebAssembly tail-call instructions to the Kotlin/Wasm backend. The compiler can now detect calls in tail position and emit return_call or return_call_ref, helping recursive Kotlin/Wasm programs avoid increasing the call stack.

In Ayako’s benchmarks, several recursive patterns became 1.7–4.3x faster at a recursion depth of 10,000. At a depth of one million, the same programs crashed without tail calls and completed successfully with them.

Testing the change on real-world projects also revealed an unexpected performance regression in V8. Ayako traced it to a missing optimization for return_call, submitted a fix, and had the patch merged into V8.

“What surprised me the most was that Ayako, after implementing the new WebAssembly instructions and using them in the Kotlin backend, actually found a bug in the Google V8 engine. Not only did she report the bug, she fixed it as well.”

Charlie Zhang

Ayako has continued working on follow-up optimizations and other approaches to supporting recursive code beyond the original GSoC project.

For Ayako, GSoC 2026 was also a chance to work much more closely on language and runtime internals than in her everyday work.

“In my day job, I rarely get to touch the internals of a language, so I simply had a lot of fun with this opportunity. While investigating the slowdown, I had to read not only the compiler but also V8, and I realized how much there is to learn beyond the code I usually work on.”

Ayako Hayasaka

Read Ayako’s full story → Final project report

Mapping the global Kotlin education landscape

Contributor: Mark Seif Khalil
Mentors: Ksenia Shneyveys (JetBrains) and Elizaveta Artser (JetBrains)

Mark’s project set out to create a structured overview of where and in what context Kotlin is being taught, considering that the information is spread across websites, course curricula, repositories, learning platforms, and other sources. The project brought that fragmented information together and created a structured and automated way to gather this data.

Over the course of GSoC 2026, Mark explored different sources and approaches to collecting this information, built a database, and developed a process for parsing and structuring data from multiple sources.

“The biggest thing I learned is when to stop pushing on something that is not working and change my approach. This is a lesson I will keep with me in every project.”

Mark Seif Khalil

The resulting project gives us a reusable foundation for monitoring Kotlin’s presence in education and identifying trends and gaps.

“What impressed us both the most about Mark was his ability to take an initially exploratory idea and bring his own vision for the research while continuously incorporating our feedback. Mark turned this scattered information into a resource we can actually use to understand Kotlin education worldwide.”

Ksenia Shneyveys, Elizaveta Artser

Read Mark’s full story → Kotlin Education Landscape
Watch Mark’s GSoC reflection

Interested in contributing to Kotlin through a future Google Summer of Code – or mentoring a project yourself?

Join the #gsoc channel in the Kotlin Slack to meet the community, ask questions, and follow future GSoC announcements.