Java 27 vs Java 26: What Changed Between JDK 26 and JDK 27

Java 27 vs Java 26 compared in plain language — full JEP lists, which previews advanced, what Java 27 makes default, what Java 26 removed, and which to use.

Java 27 vs Java 26 is a useful comparison for any team tracking Java’s six-month release train. Both are recent, both are non-LTS, and they arrived just half a year apart. Yet the two releases play very different roles. Java 26 was a tidy, incremental step. Java 27 took several long-running experiments and switched them on by default.

Java 26 landed on March 17, 2026. Java 27 followed on September 15, 2026. Neither is a long-term-support version, so most production teams stay on Java 25 LTS and watch these two closely. Still, knowing what changed between them helps you plan smarter and pick the right release to test against.

This article breaks down the differences in plain language. We will list every JEP in each release, show which features moved forward, and call out what Java 27 makes default that Java 26 did not. If you want the deeper Java 27 story on its own, our companion guide on Java 27 features walks through all nine JEPs with examples.

Let us start with the short version, then dig into each area.

What This Guide Covers

Here is the ground we will cover:

• A quick side-by-side of both releases at a glance.
• The key differences, listed by theme.
• The full JEP list for each version, with status.
• Which preview features advanced one round from 26 to 27.
• What Java 27 turns on by default that Java 26 did not.
• What Java 26 delivered that carries forward into 27.
• How the upgrade path looks, and which release to target.

1. Java 27 vs Java 26 at a Glance

Before the details, here is the high-level view. This table frames everything that follows.

Both releases carry four preview features and one incubator. The counts look almost identical. The real gap is what each one made permanent or default, which the rest of this guide unpacks.

2. Understanding the Release Cadence and LTS

To compare Java 27 and Java 26 fairly, you first need to understand where they sit in Java’s release model. This part trips up a lot of teams, so let us keep it simple.

Java ships a new feature release every six months. Java 25 came in September 2025. Then Java 26 followed in March 2026, and Java 27 arrived in September 2026. The next one, Java 28, is due around March 2027. The clock is steady, and you can plan around it.

2.1 LTS vs Non-LTS in Plain Words

Not every release is equal in support. Some are long-term-support, or LTS. Others are short-term, often called non-LTS. The difference is how long Oracle backs them.

• An LTS release gets years of updates. Teams build production on it and stay there for a long time. Java 25 is the current LTS.
• A non-LTS release gets about six months of premier support, then the next version takes over. Java 26 and Java 27 are both non-LTS.

So Java 26 and Java 27 are siblings in the same short-term family. Neither is meant to be a long-term home. They are more like preview windows into what the next LTS will likely contain.

2.2 Why This Matters for the Comparison

Here is the practical point. Because both are non-LTS, the question is rarely “which one do we run for years?” It is “which one do we test against right now?” That reframes the whole comparison.

Features often appear first in a non-LTS release as a preview, get refined over a few rounds, and then become final in a later LTS. Watching Java 26 and Java 27 is really watching the road to the next LTS. Keep that lens as we go through the differences.

💡 Interview Insight

A frequent question: “Why would a team care about a non-LTS Java release?” Non-LTS releases like Java 26 and Java 27 preview the features and defaults that a future LTS will likely adopt. Testing against them early surfaces compatibility and performance issues before the big LTS migration, even if production stays on Java 25 LTS.

3. Key Differences Between Java 26 and Java 27

Here is the comparison boiled down to the points that matter in real systems. Each one gets a fuller treatment further down.

• Release role — Java 26 was mostly cleanup and preview rounds. Java 27 promoted several features to standard, on by default.
• Garbage collection — Java 26 tuned G1 for throughput (JEP 522). Java 27 made G1 the default collector everywhere (JEP 523).
• Memory footprint — Compact object headers were not the default in Java 26. Java 27 makes them the default (JEP 534), shrinking headers from 96 to 64 bits.
• Security — Java 27 adds post-quantum TLS (JEP 527) and JFR data redaction (JEP 536). Neither existed in Java 26.
• Preview progress — Primitive patterns, structured concurrency, lazy constants, and PEM all moved one preview round forward in Java 27.
• Networking and startup — Java 26 added HTTP/3 (JEP 517) and AOT object caching with any GC (JEP 516). These carry into Java 27 unchanged.
• Cleanup — Java 26 removed the Applet API (JEP 504) and started tightening final fields (JEP 500). Both are one-time changes.
• Overall takeaway — Java 26 set the stage; Java 27 flipped the switches. Java 27 is the fuller release.

💡 Interview Insight

A common question: “What is the biggest difference between Java 26 and Java 27?” Java 26 was incremental — preview rounds plus cleanup like the Applet API removal. Java 27 promoted long-running work to default: G1 everywhere and compact object headers, plus new post-quantum TLS and JFR redaction. Both are non-LTS with four previews and one incubator each.

4. The Full JEP List for Each Release

Every Java release is defined by its JEPs, short for JDK Enhancement Proposals. Listing both sets side by side makes the pattern easy to spot.

4.1 Java 26 JEPs

Java 26 shipped ten JEPs. Here they are:

4.2 Java 27 JEPs

Java 27 shipped nine JEPs. Here they are:

Look closely and a theme jumps out. Several features appear in both lists, just one preview round further along in Java 27. Others are brand new to 27. And a couple of Java 26 items are one-time cleanups that do not repeat. Let us break these groups apart.

💡 Interview Insight

Expect: “How many JEPs did Java 26 and Java 27 ship?” Java 26 delivered ten JEPs; Java 27 delivered nine. Both are non-LTS releases with four preview features and one incubator each. The key difference is direction: Java 26 leaned on cleanup and preview rounds, while Java 27 promoted several features to default behaviour.

5. Features That Advanced From Java 26 to Java 27

Five features live in both releases. In each case, Java 27 carries the same feature one preview or incubator round further. This is how Java matures a feature slowly, gathering feedback before it becomes permanent. If you are choosing between the two, none of these became final in either version.

5.1 Primitive Types in Patterns

This feature lets pattern matching, instanceof, and switch work with primitive types like int and double, not just objects. In Java 26 it was the fourth preview, as JEP 530. In Java 27 it moves to the fifth preview, as JEP 532.

The Java 27 round tightens the rules further. It refines the definition of exactness for safe conversions and applies stricter dominance checks in switch. The goal stays the same across both releases: make the type system more uniform and catch more coding errors at compile time.

double value = 42.0;

if (value instanceof int i) {
    System.out.println("Exact integer value: " + i);
}

The switch side is where this feels most useful. You can now branch on a primitive value and bind it in one clean step, guards included:

static String classify(double value) {
    return switch (value) {
        case 0.0 -> "zero";
        case double d when d < 0 -> "negative";
        case double d -> "positive: " + d;
    };
}

Before this feature, mixing primitive checks and casts in a switch was awkward. You often fell back to chains of if-else with manual casting. The primitive-pattern version reads better and lets the compiler catch mistakes for you.

Since it is still a preview in both versions, you compile and run it with preview features enabled. The direction here ties into Project Valhalla, Java’s long-term effort to unify primitives and objects. When Valhalla lands, this groundwork should make the whole type system feel more consistent.

5.2 Structured Concurrency

Structured concurrency treats a group of related concurrent tasks as one unit of work. In Java 26 it was the sixth preview, as JEP 525. In Java 27 it becomes the seventh preview, as JEP 533.

The Java 27 round refined how exceptions flow out of a task scope. In earlier previews, the standard joiners used a different failure exception. In Java 27, they throw an ExecutionException, with the original cause reachable through getCause(). The join() method also carries a clearer exception type in its signature.

A simple example makes the idea clear. Say an endpoint needs three pieces of data at once. With structured concurrency, you fork them inside a scope and join as one unit:

try (var scope = StructuredTaskScope.open()) {
    var customer = scope.fork(() -> loadCustomer());
    var orders   = scope.fork(() -> loadOrders());
    var recs     = scope.fork(() -> loadRecommendations());

    scope.join();  // wait for all as one unit

    return combine(customer.get(), orders.get(), recs.get());
}

When the scope closes, every child task is guaranteed to be done. Nothing leaks into the background. If one task fails, the group is handled together instead of leaving orphaned threads behind.

This pairs naturally with virtual threads, which went standard back in Java 21. Virtual threads make many concurrent tasks cheap. Structured concurrency organizes those related tasks into one clean lifecycle. Together they give server code a much clearer concurrency model.

Why does it stay in preview so long? Concurrency APIs are very hard to change once they are final, so the team keeps refining based on real feedback rather than rushing. That patience is a good sign, not a red flag.

5.3 Lazy Constants

A lazy constant holds a single value that is built only on first use, then stays fixed. In Java 26 it was the second preview, as JEP 526. In Java 27 it becomes the third preview, as JEP 531.

This feature has an interesting history. It started life as “Stable Values” and was renamed to “Lazy Constants,” with the API simplified along the way. Java 27 continues that polish, including how the value behaves when its computing function fails.

private static final LazyConstant<SearchModel> MODEL =
        LazyConstant.of(SearchModel::load);

static Result search(String query) {
    return MODEL.get().search(query);
}

The value is treated like a final field by the JVM, so it gets the same optimizations, while still letting you delay expensive setup until first use. That makes it attractive for cloud-native apps that restart and autoscale often.

5.4 PEM Encodings and the Vector API

Two more features advanced by exactly one round each:

• PEM Encodings of Cryptographic Objects: second preview in Java 26 (JEP 524), third preview in Java 27 (JEP 538). This adds a standard API to encode and decode keys, certificates, and CRLs in the common PEM format, using PEMEncoder and PEMDecoder.
• Vector API: eleventh incubator in Java 26 (JEP 529), twelfth incubator in Java 27 (JEP 537). This lets you write explicit SIMD-style computations in portable Java. It stays in incubation, waiting on Project Valhalla.

So five features in total moved forward one step from 26 to 27. None of them became final in either release. They keep evolving, one careful round at a time.

💡 Interview Insight

Expect: “Which preview features advanced from Java 26 to Java 27?” Primitive patterns went from fourth to fifth preview, structured concurrency from sixth to seventh, lazy constants from second to third, and PEM encodings from second to third. The Vector API moved from eleventh to twelfth incubator. None were finalized in either release.

6. What Java 27 Turns On by Default That Java 26 Did Not

Now the part that really separates the two. Java 27 introduced several features that simply were not in Java 26. Three of them are standard, meaning they are on by default with no flag needed. This is where you feel the biggest change just by upgrading the JVM.

6.1 G1 as the Default Garbage Collector Everywhere

In Java 26 and earlier, the JVM picked a garbage collector based on the environment. On small or constrained setups, it could quietly fall back to Serial GC. Java 27 changes this with JEP 523.

Now G1 is the default in every environment, unless you choose another collector yourself. So the same app behaves more consistently across your laptop, staging, and tiny containers.

You can still opt into Serial GC when you want it:

-XX:+UseSerialGC

Why does this matter in practice? Consistency. Imagine you build and load-test a service on your laptop, then deploy it into a container with tight CPU and memory limits. In Java 26 and before, that resource gap could flip the JVM to Serial GC automatically. The same app, launched the same way, could behave differently across environments.

Teams often did not even notice, because the workload was small. But garbage-collection behaviour drives pause times and throughput, so a silent switch is a real risk. Java 27 removes that surprise. No collector specified now means G1, everywhere.

If you want to confirm which collector is active, a quick check helps:

java -Xlog:gc -version

Notice the link back to Java 26. Its JEP 522 improved G1 throughput by reducing synchronization between application and collector threads. That work helped make G1 strong enough to become the universal default in Java 27. One release set up the next. It is a nice example of how the six-month cadence lets each version build on the last.

6.2 Compact Object Headers by Default

This is one of the most practical differences. Every Java object carries a header of metadata. On 64-bit JVMs, that header traditionally used 96 bits, which is 12 bytes.

Java 27 makes compact object headers the default with JEP 534, shrinking the header to 64 bits, or 8 bytes. In Java 26, this compact layout existed but was not the default. Java 27 flips the switch for everyone.

Four bytes sounds tiny. But think about scale. A large Spring Boot service can hold millions of objects. Data-heavy apps can hold tens or hundreds of millions. Domain entities, caches, JSON models, ORM-managed objects, framework metadata. They all pile up fast.

For apps holding millions of objects, that adds up. Independent benchmarks such as SPECjbb2015 have reported around 22 percent less heap and roughly 8 percent less CPU time with the smaller header. Real savings vary with object alignment, so do not assume every object shrinks by exactly four bytes. Still, the direction is a clear win.

Smaller objects bring bonus wins beyond raw memory too:

• More objects fit into CPU caches, which helps speed.
• More objects fit inside the same heap regions.
• Less memory has to be scanned during garbage collection.
• Each JVM may need less memory, so container density improves.

If testing ever turns up a problem, you can turn it back off:

-XX:-UseCompactObjectHeaders

For most teams, though, the best part is that there is nothing to rewrite. Upgrade the JVM, and your objects simply take less space. This is the kind of win that Java 26 users do not get by default, and Java 27 users do.

6.3 Two New Security and Diagnostics Features

Java 27 also brings two security-focused features that Java 26 did not have:

• Post-Quantum Hybrid Key Exchange for TLS 1.3 (JEP 527): TLS 1.3 can now combine a classic elliptic-curve algorithm with the post-quantum ML-KEM algorithm. The group X25519MLKEM768 is on by default, so many apps gain protection with no code changes.
• JFR In-Process Data Redaction (JEP 536): Java Flight Recorder can now strip sensitive command-line arguments, environment variables, and system properties before the data leaves the process, keeping secrets out of shared recordings.

The post-quantum piece is worth dwelling on. There is a real threat called “harvest now, decrypt later.” An attacker records your encrypted traffic today, stores it, and tries to crack it years later once quantum computers are strong enough. Hybrid key exchange defends against that by combining a classic algorithm with a quantum-resistant one. If one weakens over time, the other still guards the connection.

The JFR redaction piece solves a quieter but common problem. Flight Recorder files are often shared with support teams and vendors. Those files can contain passwords or tokens passed as arguments or environment variables. Java 27 strips them before the data leaves the process, so a shared recording no longer leaks secrets by accident.

Both are standard features in Java 27. Neither existed in Java 26. So on security, Java 27 is a clear step forward, and both improvements land without you writing new code.

💡 Interview Insight

A strong question: “What does Java 27 make default that Java 26 did not?” Java 27 makes G1 the default garbage collector in all environments (JEP 523) and makes compact object headers the default layout (JEP 534), cutting object headers from 96 to 64 bits. It also adds post-quantum TLS (JEP 527) and JFR redaction (JEP 536), neither of which was in Java 26.

7. What Java 26 Delivered That Carries Into Java 27

The comparison runs both ways. Java 26 shipped several standard features that are simply part of the platform now. They do not reappear as JEPs in Java 27 because the work was already done. If you jump straight from Java 25 to Java 27, you still inherit all of them.

7.1 HTTP/3 for the HTTP Client API

Java 26 added HTTP/3 support to the HTTP Client API with JEP 517. Your applications and libraries can talk to HTTP/3 servers with minimal code change. This is a real networking upgrade that arrived in Java 26 and stays available in Java 27 as normal behaviour.

7.2 Ahead-of-Time Object Caching with Any GC

Java 26 extended ahead-of-time object caching to work with any garbage collector, including ZGC, through JEP 516. This is part of Project Leyden and helps applications start up faster. Startup and warmup time matter a lot in cloud fleets that scale up and down, so this one is quietly valuable. It carries forward into Java 27.

7.3 Prepare to Make Final Mean Final

Java 26’s JEP 500 started tightening how final fields work. It issues warnings when code uses deep reflection to mutate a final field. The aim is Java’s “integrity by default” principle, moving toward a future where final truly means final.

This matters for some serialization libraries and frameworks that rely on that trick. It is a Java 26 change, and the tightening continues quietly beyond it. Worth knowing about if you maintain such a library.

7.4 Removing the Applet API

Java 26 removed the old Applet API entirely with JEP 504. It had been deprecated for removal since Java 17. If your code somehow still referenced it, Java 26 is where it stopped compiling.

This is a one-time cleanup, so it does not appear in Java 27. But if you jump from Java 25 to Java 27, remember this removal happened along the way.

💡 Interview Insight

You might get: “What standard features did Java 26 add that are not JEPs in Java 27?” Java 26 delivered HTTP/3 for the HTTP Client (JEP 517), AOT object caching with any GC including ZGC (JEP 516), final-field mutation warnings (JEP 500), and removal of the Applet API (JEP 504). These are one-time additions that carry into Java 27 as normal platform behaviour.

8. Performance: How the Two Releases Stack Up

Performance is where most teams feel a Java upgrade. So it is worth pulling the performance-related changes together and comparing them side by side.

8.1 Garbage Collection

Java 26 made G1 faster through JEP 522, which cut synchronization between application and collector threads. That is a throughput gain for anyone already on G1.

Java 27 went further and made G1 the default in every environment. So Java 26 tuned the engine, and Java 27 put that engine in every car. If you run small containers that used to fall back to Serial GC, this is the bigger change of the two.

8.2 Memory Footprint

On memory, Java 27 is the clear leader. Compact object headers become the default, trimming each object’s header by four bytes. Across object-heavy workloads, that can mean noticeably smaller heaps and better cache behaviour.

Java 26 had the compact-header option available, but not on by default. So a Java 26 team had to opt in with a flag to see the benefit. A Java 27 team gets it automatically.

8.3 Startup and Warmup

Here Java 26 actually leads on the new arrival. Its JEP 516 extended ahead-of-time object caching to work with any garbage collector, including ZGC. That helps applications start and warm up faster, which matters a lot in autoscaled cloud fleets.

Java 27 does not add a new startup JEP, but it keeps the Java 26 work. So if you move from Java 25 straight to Java 27, you pick up this startup improvement along the way.

8.4 A Quick Performance Summary

Put simply, the performance story splits cleanly:

• Garbage collection consistency: Java 27 wins, with G1 everywhere by default.
• Memory footprint: Java 27 wins, with compact headers on by default.
• Startup and warmup: Java 26 introduced the AOT caching gain, and Java 27 keeps it.
• Raw G1 throughput: introduced in Java 26, still present in Java 27.

So Java 27 holds every performance gain Java 26 had, and adds default memory and consistency wins on top. That is a big reason it is the fuller release.

💡 Interview Insight

A performance-focused question: “Which release gives better out-of-the-box performance, Java 26 or Java 27?” Java 27, in most cases. It keeps Java 26’s G1 throughput work and AOT startup caching, then adds compact object headers by default and G1 as the universal default collector. Java 26 users had to opt into compact headers with a flag.

9. Upgrade Paths: Which Jump Are You Making?

How big is the move? It depends on where you start. Let us look at both common paths, since they carry very different testing loads.

9.1 Upgrading From Java 26 to Java 27

If you already run Java 26, moving to Java 27 is a smaller step. You mostly gain the new defaults and two new security features. The main things to test are:

• G1 now default in constrained environments where Serial GC used to kick in.
• Compact object headers now on by default, so check memory and layout behaviour.
• The newer preview rounds if you use primitive patterns, structured concurrency, lazy constants, or PEM.

None of this should force code changes. It is mostly benchmarking and confirming behaviour under your real workloads.

9.2 Upgrading From Java 25 LTS Straight to Java 27

Many teams skip non-LTS releases and sit on Java 25. If that is you, jumping straight to Java 27 means you inherit everything from Java 26 too. So your testing list grows to include:

• HTTP/3 support and the AOT object caching changes from Java 26.
• Final-field mutation warnings from Java 26, which may affect some libraries.
• The Applet API removal from Java 26, if any old code still used it.
• All the Java 27 defaults: G1 everywhere, compact headers, post-quantum TLS, and JFR redaction.

This is the honest catch with non-LTS releases. Skipping one does not skip its changes. They pile up and land together at your next upgrade, so plan the test cycle accordingly.

9.3 A Short Testing Checklist

Whichever path you take, a few checks pay off before you trust a new JVM in production:

• Benchmark garbage collection under realistic CPU and memory limits, especially in small containers.
• Measure memory footprint with compact headers on, since gains depend on object layout.
• Confirm your JFR secret-naming conventions are covered by the new redaction filters.
• Pin preview and incubator flags per module if you use those features.
• Watch startup and warmup time, which the Java 26 AOT work can help.

10. Java 27 vs Java 26: Which Should You Use?

Both Java 26 and Java 27 are non-LTS. Each got six months of premier support. Java 26’s window ran until Java 27 superseded it, and Java 27 runs until Java 28 arrives around March 2027.

For most production teams, the base is still Java 25 LTS. So the real question is which short-term release to test against, not which to run long-term.

10.1 A Simple Way to Decide

Here is a practical way to think about it:

• If you want the latest and are actively evaluating, use Java 27. It is newer, has the default performance wins, and points to where the next LTS is heading.
• If you were already testing on Java 26, there is little reason to stay behind. Java 27 includes its forward progress plus more.
• If you run production on Java 25 LTS, use Java 27 as your evaluation release so you preview both 26 and 27 changes at once.

In short, when choosing between the two today, Java 27 is usually the better target. It is the more complete of the pair and sets you up for the next LTS.

💡 Interview Insight

Likely: “Between Java 26 and Java 27, which should a team target?” Both are non-LTS with six months of support. Java 27 is generally the better choice today because it includes Java 26’s progress plus new defaults like G1 everywhere and compact object headers. Most teams keep Java 25 LTS in production and use Java 27 as their evaluation release.

11. FAQ’s on Java 27 vs Java 26

12. Final Thoughts

So how do Java 27 and Java 26 really compare? They sit six months apart and share the same non-LTS status, yet they play different roles.

Java 26 was a tidy release. It advanced several preview features by one round, added HTTP/3 and AOT object caching, warned about final-field mutation, and removed the old Applet API. Solid, steady, incremental.

Java 27 took the next step and made big things default. G1 everywhere, compact object headers, post-quantum TLS, and JFR redaction all landed as standard. It also carried the shared preview features one round further.

The pattern between them is worth remembering. Java 26 set the stage, and Java 27 flipped several switches. Its own JEP 522 G1 work in Java 26, for example, helped G1 become the universal default in Java 27. Each release builds on the one before it.

If you are choosing today, Java 27 is the fuller release and the smarter target for evaluation. But whichever you test, the direction is clear. Java keeps getting faster, safer, and more consistent, one careful six-month step at a time.

12. Further Reading

• Java 27 Features Explained: What’s New in JDK 27 with Examples
• The Arrival of Java 27 — Oracle Java Blog
• The Arrival of Java 26 — Oracle Java Blog
• JEP 523: Make G1 the Default Garbage Collector in All Environments
• JEP 534: Compact Object Headers by Default
• Structured Concurrency and Virtual Threads in Java