Why Migrate to the Latest IBM Semeru Runtime on z/OS?
Java continues to be a cornerstone of enterprise computing, powering mission-critical workloads across banking, insurance, government, and beyond. If your organization is still running IBM SDK for z/OS, Version 8 (IBM SDK 8), or an earlier version of IBM Semeru Runtime Certified Edition for z/OS, now is the time to modernize!
With IBM Semeru Runtime Certified Edition for z/OS, Version 25 now generally available, this blog outlines why migrating to the latest Semeru version is not just a good idea, but is essential for the security, performance, and longevity of your enterprise applications.
Why Make the Change?
The Java ecosystem moves fast. Staying on aging versions (especially IBM SDK 8) exposes your organization to growing risks and missed opportunities. Here's why upgrading to the latest IBM Semeru Runtime matters:
Security: Stay Ahead of Threats
Older Java versions eventually reach End of Service (EOS), after which they exit the standard support lifecycle. For IBM SDK 8 on z/OS, EOS is September 2026, with Extended End of Service (EEOS) available through December 2030.
Remaining on older Java levels increases long‑term risk, cost, and operational complexity, and limits access to the latest security improvements, performance enhancements, and ecosystem compatibility delivered in newer Java releases.
Semeru 25 on z/OS delivers access to the latest Java security capabilities and standards, including:
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Post‑Quantum Cryptography (PQC): Support for ML‑KEM and ML‑DSA algorithms designed to address security risks posed by future quantum computing.
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Java Security Providers: Support for IBM and OpenJDK providers, including IBMJCECCA, IBMZSecurity, IBMJCEHYBRID, OpenJCEPlus, SunPKCS11, and JAAS.
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IBM Z Crypto Integration: Exploitation of IBM Z cryptographic hardware for secure workloads.
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Security Maintenance: Ongoing security fixes from OpenJDK and Eclipse OpenJ9.
Performance: Do More with Your Existing Hardware
Each Semeru release delivers new JVM performance enhancements. Semeru 25 goes further with hardware-level optimizations specifically tuned for IBM Z:
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Improved throughput for Java workloads using new hardware instructions on IBM z17 (see blog)
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Enhanced SSL performance for secure workloads.
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Accelerated COBOL-to-Java modernization (faster processing of COBOL Copybook data within Java applications)
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Compiler modernization via IBM Open XL C/C++ compiler and delivering measurable performance improvements, including up to 8% faster startup time, resulting in a more responsive Java runtime on z/OS (see blog for more details)
These gains translate to real-world benefits: faster transaction throughput, lower CPU consumption, and reduced cloud computing costs.
Ecosystem Compatibility: Stay Current
Third-party libraries, frameworks, and tools (Spring, Jakarta EE, Kafka, and more) frequently drop support for older Java versions. Running IBM SDK 8 or Semeru 11 today could mean being locked out of important library updates, security fixes, and new functionality that your development teams need.
With Semeru 25, you're on the latest LTS release, ensuring compatibility with the latest tooling, frameworks, and runtime platforms. In addition, many Java dependent z/OS components and middleware are aligned to provide Day 1 support, including CICS, IMS, Liberty, Db2, MQ, and more (see list).
What's New in Semeru 25?
IBM Semeru Runtime Certified Edition for z/OS, Version 25 is a fully certified Java runtime and development kit based on the Java SE 25 specification. It incorporates OpenJDK class libraries and the Eclipse OpenJ9 JVM, and it adds IBM-specific extensions tailored for IBM Z.
Key Highlights include:
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Standards Compliance: Certified with the Java Compatibility Kit (JCK), ensuring full adherence to Java SE 25 specifications and seamless application portability across platforms.
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Performance on IBM z17: New hardware instruction exploitations, enhanced SSL throughput, and accelerated COBOL Copybook processing.
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Post-Quantum Cryptography: ML-KEM and ML-DSA support aligned with NIST standards, securing your data against future quantum threats.
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JZOS Enhancements: Enhanced JZOS Batch Launcher and Toolkit, with JZOS libraries now available via Maven Central for streamlined development workflows.
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JDK Flight Recorder (JFR): Low-overhead monitoring and diagnostics capturing JVM and application metrics (i.e. CPU usage, GC pauses, lock contention) with JDK Mission Control (JMC) for visualization and tuning.
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Foreign Function & Memory (FFM) API: FFM support in Java 25 enables safer, more efficient native interoperability without JNI, unlocking modern integration scenarios with native libraries on z/OS.
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Improved Runtime Performance: Better startup and garbage collection performance driven by compiler and runtime optimizations, providing measurable gains for Java workloads on z/OS.
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Zero License Charge: Available at no license charge through Shopz (5655-JB2) SMP/E or as a downloadable non-SMP/E Pax.
What Version of Semeru Should I Upgrade To?
If you are currently running IBM SDK 8, the recommended migration targets are Semeru 21 or Semeru 25:
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Semeru 21 is a widely adopted long‑term support (LTS) release and is a strong choice for customers looking for stability and maturity.
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Semeru 25 is the latest LTS release and is the preferred target if your goal is to maximize long‑term support, ecosystem compatibility, and time before the next required migration.
In most cases, there is no need to migrate to Semeru 11 or 17 as intermediate steps. The migration effort from IBM SDK 8 to Semeru 21 or 25 is comparable, and moving directly to a newer LTS avoids unnecessary additional testing and follow‑on migrations.
When migrating to Semeru 21 or later, customers should validate their applications against API, behaviour, and default changes introduced across Java releases. These should be validated through proper testing, but they do not require stepping through earlier Java versions.
What to Keep in Mind Before Migrating
Migration is not without its considerations. Java versions introduce changes that may require application review:
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Test your applications, libraries, and frameworks thoroughly against the target Semeru version before deploying to production.
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Review Oracle's JDK migration guides and IBM's version-specific migration documentation to understand deprecated or removed APIs.
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Java 21 introduced JEP 400 (UTF-8 by default), which may require code changes if you rely on platform-default encoding behaviour.
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Starting with Semeru 11, the Java runtime is modularized; applications using internal JDK APIs or removed modules may need updates (link).
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Plan for incremental testing: validate applications in non‑production environments (such as development, test, or staging) before deploying the new Java level to production workloads.
IBM provides comprehensive migration guides and upgrade portal tooling to support your journey. Leveraging these resources will significantly reduce the time and risk associated with the transition.
Benefits at a Glance
Migrating to the latest Semeru version enables you to:
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Leverage the newest Java language features, OpenJDK class libraries, and the Eclipse OpenJ9 virtual machine.
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Secure applications with post-quantum cryptographic operations and enhanced IBM Z security provider support.
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Use modern Java APIs, libraries, and frameworks for a consistent hybrid cloud experience.
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Accelerate performance with the latest JIT, GC, and hardware-level optimizations on IBM Z.
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Ensure continued support and active maintenance through IBM's LTS commitment.
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Access Day 1 ecosystem support across CICS, IMS, Liberty, Db2, MQ, and more.
Conclusion
The question is no longer whether to migrate from IBM SDK 8 or an older Semeru version - it's when. Every quarter that passes on an aging runtime is a quarter of security risk, performance left on the table, and growing technical debt. With Semeru 25 now generally available and backed by Day 1 ecosystem support across the z/OS software stack, there has never been a better time to make the move.
Take the first step today - your applications, your users, and your operations team will thank you.
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