Project Leyden

The primary goal of this Project is to improve the startup time, time to peak performance, and footprint of Java programs.

This Project is sponsored by the HotSpot and Core Libraries Groups.

JEP status

In progress:

• TBD: Ahead-of-Time Code Compilation

Delivered:

• 483: Ahead-of-Time Class Loading & Linking (JDK24)
• 514: Ahead-of-Time Command-Line Ergonomics (JDK25)
• 515: Ahead-of-Time Method Profiling (JDK25)
• 516: Ahead-of-Time Object Caching with Any GC (JDK26)

Development

Development takes place in our OpenJDK GitHub repository, openjdk/leyden. Most of our current work is in the premain branch. From that branch we occasionally publish early-access builds at jdk.java.net/leyden, along with release notes. Please try out the builds and let us know what you think! You can send feedback to the leyden-dev mailing list (subscribe to the list before posting).

Design notes

• Thoughts on Training Runs (2024/9)
• Condensing Indy Bootstraps (2023/8)
• Toward Condensers (2023/7)
• Selectively Shifting and Constraining Computation (2022/10)
• Project Leyden: Beginnings (2022/5)

Presentations

• Ahead of time, the final frontier
  Mara Arias de Reyna, Andrew Dinn JChampions Conference 2026 (video)

• Project Leydens AOT: Shifting Startup into High Gear
  Dan Heidinga, JavaOne 2025 (video)

• Project Leyden: Improving Javas Startup Time
  Per Minborg, Sbastien Deleuze, Devoxx BE 2024 (video)

• Project Leyden Update
  Ioi Lam, Dan Heidinga, JVMLS2024 (video)

• Project Leyden: Capturing Lightning in a Bottle
  Per Minborg, DevoxxUK 2024 (video)

• Choose Your Own Performance, a Project Leyden Update
  Dan Heidinga, DevNexus2024 (video, slides)

• Premain Case Study: Spring PetClinic
  Vladimir Ivanov, 2023/9 (slides)

• Project Leyden: Capturing Lightning in a Bottle
  Mark Reinhold, John Rose, JVMLS2023 (video, slides)

Resources

• Mailing list: leyden-dev
• Repository: openjdk/leyden
• Early access builds: jdk.java.net/leyden (release notes)