Virtual threads are stable in Java 25, but they are not new to it: they became a standard feature in JDK 21. They can help applications handle more concurrent, waiting work—especially I/O-heavy server tasks—but they do not make individual tasks or CPU-bound code run faster. Java 25 adds separate improvements for startup, memory use, concurrency context, and diagnostics; whether any improves your application depends on its workload.
Are virtual threads stable in Java 25?
Yes. Virtual threads were delivered as a stable feature in JDK 21 under JEP 444. Java 25 does not newly stabilize them. A virtual thread is a java.lang.Thread that is not tied to one operating-system thread for its entire lifetime. The JDK can schedule many virtual threads over a smaller number of platform threads.
This design lets developers keep a straightforward thread-per-task programming style while supporting many concurrent tasks. It is particularly relevant to servers handling numerous requests that spend time waiting for I/O or other blocking operations.
Do virtual threads make Java code faster?
Not in the sense of making an individual thread execute instructions faster. JEP 444 puts it plainly: “Virtual threads are not faster threads.” Their potential benefit is greater concurrency and aggregate throughput for workloads with substantial waiting—not automatically lower latency for each request or faster computation.
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| Workload or goal | What virtual threads may change | What to watch |
|---|---|---|
| Many concurrent I/O-bound tasks | May allow more tasks to wait concurrently without requiring one platform thread per task. | Throughput and latency still depend on CPU, memory, connection pools, downstream services, and other limits. |
| CPU-bound computation | Do not make the computation itself run faster. | Adding threads beyond available processor capacity does not create more processing capacity. |
| Request latency | May help indirectly if constrained concurrency is causing queuing. | Do not assume lower per-request latency; identify the actual bottleneck and measure. |
Create virtual threads per task rather than treating them as scarce platform threads to pool. That does not mean the rest of the system has unlimited capacity: use suitable resource limits and back-pressure so a surge of concurrent work does not overwhelm databases, remote services, memory, or connection pools.
Blocking behavior and pinning
JEP 444 describes pinning when a virtual thread blocks while executing synchronized code or native or foreign code. Frequent, long-lived pinning can interfere with the intended scheduling benefits, so investigate it on important blocking paths rather than rewriting all synchronized code pre-emptively. Consult the documentation for the exact JDK build you deploy when assessing current runtime behavior.
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What concurrency-related APIs changed in Java 25?
Scoped Values are final
Scoped Values became a final API in JDK 25. They let a method pass immutable data to callees and child threads for a bounded call scope. This can be useful alongside virtual threads when request context or similar data needs to flow through a call chain. Oracle describes them as easier to reason about than thread-local variables and as offering lower space and time costs in relevant use cases (Oracle’s JDK 25 migration guide).
Consider them when data is immutable and passed one way through a bounded scope. They are not a universal replacement for ThreadLocal; check how existing code reads, changes, and retains thread-local state before migrating it. Inside.java’s overview of JDK 25 performance changes describes scoped sharing as avoiding per-thread copies in use cases where ThreadLocal serves a similar purpose.
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Other concurrency and data APIs remain preview or incubating
| Feature | Java 25 status | Adoption implication |
|---|---|---|
| Structured Concurrency | Preview API, fifth preview | Preview APIs can change; do not treat this as a finalized interface. |
| Stable Values | Preview API | Evaluate with preview-feature compatibility in mind. |
| Vector API | Incubator feature | Incubator status is distinct from a final Java API. |
Check the JDK 25 feature and migration notes for the status and requirements applicable to your build.
Which Java 25 performance improvements may matter?
Java 25 includes changes with different targets. The potential gain from one area—such as startup—should not be presented as a general improvement in steady-state throughput. Oracle’s significant changes guide and JDK 25 release announcement describe the changes; none establishes a universal speedup for arbitrary applications.
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| Change | What it targets | Qualification |
|---|---|---|
| Compact object headers | Memory footprint and potentially data locality | Oracle’s JDK 25 migration guide says HotSpot object headers on 64-bit architectures are reduced to 64 bits from prior 96- or 128-bit sizes. Actual effects depend on object layout and workload. |
| AOT Command-Line Ergonomics | Simpler workflows for creating ahead-of-time (AOT) caches | Benefits depend on whether an application uses the cache workflow. |
| AOT Method Profiling | Startup and warmup | Profiles from a previous run can be available at VM startup so the JIT can generate native code earlier, rather than waiting to gather profiles during the current run. This is not a blanket claim of better steady-state throughput. |
| JFR CPU-Time Profiling | Diagnostics | Experimental feature specifically improving CPU-time profiling data on Linux; it is not itself an application speedup. |
| JFR Cooperative Sampling | Diagnostics | Improves stack-sampling stability and reduces safepoint bias. |
| JFR Method Timing & Tracing | Diagnostics | Supports method timing and tracing through bytecode instrumentation. |
Java 25 also has other library, compiler, and runtime changes. The Inside.java overview discusses examples including String hash behavior, but it is non-exhaustive. A claimed percentage improvement only makes sense when tied to a defined benchmark and its hardware and software setup; there is no official general percentage for virtual threads or Java 25 performance.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How should you assess virtual threads and Java 25 for your application?
- Identify the work. Map request and task boundaries, then determine whether tasks spend substantial time waiting on I/O or other blocking operations, or mostly consume CPU.
- Find the limits. Check CPU, memory, connection pools, downstream service capacity, and any existing queue or concurrency controls. More concurrent tasks do not remove these constraints.
- Review code and dependencies. Inspect ThreadLocal usage, native calls, blocking behavior, framework and library support, and how your monitoring tools represent virtual threads. Evaluate Scoped Values only for compatible immutable data passed through a bounded scope.
- Check compatibility before changing the runtime. Use the JDK 25 migration guide and consolidated release notes. Test source, binary, and behavioral compatibility: successful compilation alone does not establish identical runtime behavior.
- Compare representative runs. Test the same production-representative workload on the current JDK and JDK 25. Measure throughput, latency distributions, CPU and memory or heap use, startup and warmup, and downstream saturation. Treat results as specific to your workload and environment.
Should you upgrade to Java 25?
Consider Java 25 when its APIs or runtime changes fit your needs and your application, dependencies, and deployment environment pass compatibility and workload testing. Virtual threads alone are not a reason to upgrade: they have been stable since JDK 21, and their value depends on the shape and bottlenecks of the work you run.
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For Oracle’s distribution, the consolidated release notes list JDK 25.0.4.1, dated August 18, 2026, and recommend updating with each Critical Patch Update. Release cadence, support terms, and licensing differ by JDK vendor and can change, so consult your vendor’s current release notes and terms before a production update. See Oracle’s consolidated JDK 25 release notes.
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