diff --git a/README.md b/README.md
index 8494245..8b13668 100644
--- a/README.md
+++ b/README.md
@@ -103,3 +103,4 @@ Modules for the Java 8 / 11 / 17 / 21 feature articles, one folder each, each wi
 - `java8-features/` — see its README
 - `java11-features/` — see its README
 - `java17-features/` — see its README
+- `java21-features/` — see its README
diff --git a/java21-features/README.md b/java21-features/README.md
new file mode 100644
index 0000000..d67910f
--- /dev/null
+++ b/java21-features/README.md
@@ -0,0 +1,13 @@
+# java21-features — Java 21 features with examples
+
+Companion code for the ankurm.com article **Java 21 Features with Examples: Virtual Threads, Record Patterns, Sequenced Collections**. The explanation lives in the article; this folder holds the runnable sources and the transcripts they produced. There is no `docs/` folder: the depth is inside the article itself.
+
+```bash
+JDK21=/path/to/jdk21 ./run.sh      # regenerates output/*.txt
+```
+
+- `src/` compiles and runs unchanged on the JDK named in each output header.
+- `broken/` fails to compile on purpose; the compiler's own message is committed in `output/`.
+- `output/` is real captured output, regenerated by `run.sh`.
+
+Tested on: OpenJDK 21.0.12.1 (the preview and incubator demos need --enable-preview / --add-modules, which run.sh passes).
diff --git a/java21-features/broken/DominatedCase.java b/java21-features/broken/DominatedCase.java
new file mode 100644
index 0000000..4b5b636
--- /dev/null
+++ b/java21-features/broken/DominatedCase.java
@@ -0,0 +1,5 @@
+/** Fails to compile on purpose: a more general pattern before a specific one makes the later case unreachable. */
+public class DominatedCase {
+    static String f(Object o) { return switch (o) { case CharSequence cs -> "cs"; case String s -> "s"; default -> "d"; }; }
+    public static void main(String[] args) { }
+}
diff --git a/java21-features/broken/NonExhaustive.java b/java21-features/broken/NonExhaustive.java
new file mode 100644
index 0000000..29d2e02
--- /dev/null
+++ b/java21-features/broken/NonExhaustive.java
@@ -0,0 +1,8 @@
+/** Fails to compile on purpose: a pattern switch over a sealed type must cover every permitted subtype. */
+public class NonExhaustive {
+    sealed interface S permits A, B {}
+    record A() implements S {}
+    record B() implements S {}
+    static String f(S s) { return switch (s) { case A a -> "a"; }; }
+    public static void main(String[] args) { }
+}
diff --git a/java21-features/broken/PreviewWithoutFlag.java b/java21-features/broken/PreviewWithoutFlag.java
new file mode 100644
index 0000000..3955779
--- /dev/null
+++ b/java21-features/broken/PreviewWithoutFlag.java
@@ -0,0 +1,4 @@
+/** Fails to compile on purpose: string templates are a preview feature in 21 and are off by default. */
+public class PreviewWithoutFlag {
+    public static void main(String[] args) { String n = "x"; System.out.println(STR."hi \{n}"); }
+}
diff --git a/java21-features/output/01-virtual-threads.txt b/java21-features/output/01-virtual-threads.txt
new file mode 100644
index 0000000..e5efa4e
--- /dev/null
+++ b/java21-features/output/01-virtual-threads.txt
@@ -0,0 +1,5 @@
+$ javac  src/VirtualThreadsDemo.java && java  VirtualThreadsDemo     (21.0.12.1)
+tasks completed : 10000
+finished in < 5s: true   (10,000 x 1s sleeps)
+isVirtual       : true, daemon=true
+platform isVirtual: false
diff --git a/java21-features/output/02-record-patterns.txt b/java21-features/output/02-record-patterns.txt
new file mode 100644
index 0000000..75986e0
--- /dev/null
+++ b/java21-features/output/02-record-patterns.txt
@@ -0,0 +1,5 @@
+$ javac  src/RecordPatternsDemo.java && java  RecordPatternsDemo     (21.0.12.1)
+line from (0,0) to (3,4) length^2=25
+box of String hi
+box of Integer 7
+no match
diff --git a/java21-features/output/03-pattern-switch.txt b/java21-features/output/03-pattern-switch.txt
new file mode 100644
index 0000000..7e4fefb
--- /dev/null
+++ b/java21-features/output/03-pattern-switch.txt
@@ -0,0 +1,3 @@
+$ javac  src/PatternSwitchDemo.java && java  PatternSwitchDemo     (21.0.12.1)
+big circle | circle | square 2.0 | rect 2.0x3.0
+null handled in the switch | large int | int | string of 4 | other
diff --git a/java21-features/output/04-sequenced-collections.txt b/java21-features/output/04-sequenced-collections.txt
new file mode 100644
index 0000000..05c4bc4
--- /dev/null
+++ b/java21-features/output/04-sequenced-collections.txt
@@ -0,0 +1,11 @@
+$ javac  src/SequencedCollectionsDemo.java && java  SequencedCollectionsDemo     (21.0.12.1)
+getFirst/getLast: a c
+reversed view   : [c, b, a]
+addFirst+removeLast: [z, a, b]
+LinkedHashSet reversed: [3, 2, 1]
+firstEntry/lastEntry : x=1 z=3
+putFirst        : {w=0, x=1, y=2, z=3}
+reversed map    : {z=3, y=2, x=1, w=0}
+view sees add   : [3, 2, 1]
+immutable list : UnsupportedOperationException
+HashSet         : no getFirst (unordered)
diff --git a/java21-features/output/05-kem.txt b/java21-features/output/05-kem.txt
new file mode 100644
index 0000000..9d43685
--- /dev/null
+++ b/java21-features/output/05-kem.txt
@@ -0,0 +1,5 @@
+$ javac  src/KemDemo.java && java  KemDemo     (21.0.12.1)
+algorithm       : DHKEM
+secrets equal   : true
+secret length   : 32 bytes
+ciphertext length: 32 bytes
diff --git a/java21-features/output/06-generational-zgc.txt b/java21-features/output/06-generational-zgc.txt
new file mode 100644
index 0000000..4b5f457
--- /dev/null
+++ b/java21-features/output/06-generational-zgc.txt
@@ -0,0 +1,9 @@
+$ javac  src/GcNamesDemo.java && java -XX:+UseZGC GcNamesDemo     (21.0.12.1)
+gc bean         : ZGC Cycles
+gc bean         : ZGC Pauses
+
+$ javac  src/GcNamesDemo.java && java -XX:+UseZGC -XX:+ZGenerational GcNamesDemo     (21.0.12.1)
+gc bean         : ZGC Minor Cycles
+gc bean         : ZGC Minor Pauses
+gc bean         : ZGC Major Cycles
+gc bean         : ZGC Major Pauses
diff --git a/java21-features/output/07-vector-api.txt b/java21-features/output/07-vector-api.txt
new file mode 100644
index 0000000..6676ff9
--- /dev/null
+++ b/java21-features/output/07-vector-api.txt
@@ -0,0 +1,6 @@
+$ javac --add-modules jdk.incubator.vector src/VectorDemo.java && java --add-modules jdk.incubator.vector VectorDemo     (21.0.12.1)
+warning: using incubating module(s): jdk.incubator.vector
+1 warning
+WARNING: Using incubator modules: jdk.incubator.vector
+vector == scalar: true
+lanes >= 2      : true
diff --git a/java21-features/output/08-string-templates.txt b/java21-features/output/08-string-templates.txt
new file mode 100644
index 0000000..a8e7f54
--- /dev/null
+++ b/java21-features/output/08-string-templates.txt
@@ -0,0 +1,2 @@
+$ javac --release 21 --enable-preview src/StringTemplatesPreview.java && java --enable-preview StringTemplatesPreview     (21.0.12.1)
+Hello Ankur, 3 + 4 = 7
diff --git a/java21-features/output/09-unnamed-patterns.txt b/java21-features/output/09-unnamed-patterns.txt
new file mode 100644
index 0000000..f30e01f
--- /dev/null
+++ b/java21-features/output/09-unnamed-patterns.txt
@@ -0,0 +1,4 @@
+$ javac --release 21 --enable-preview src/UnnamedPreview.java && java --enable-preview UnnamedPreview     (21.0.12.1)
+x only         : 5
+loop count      : 3
+caught, name not needed
diff --git a/java21-features/output/10-unnamed-main.txt b/java21-features/output/10-unnamed-main.txt
new file mode 100644
index 0000000..476bf76
--- /dev/null
+++ b/java21-features/output/10-unnamed-main.txt
@@ -0,0 +1,2 @@
+$ java --enable-preview --source 21 src/UnnamedMainPreview.java     (21.0.12.1)
+no class, no static, no String[] args
diff --git a/java21-features/output/11-scoped-values.txt b/java21-features/output/11-scoped-values.txt
new file mode 100644
index 0000000..7adac9d
--- /dev/null
+++ b/java21-features/output/11-scoped-values.txt
@@ -0,0 +1,3 @@
+$ javac --release 21 --enable-preview src/ScopedValuesPreview.java && java --enable-preview ScopedValuesPreview     (21.0.12.1)
+inside handler  : user=ankur
+outside         : bound=false
diff --git a/java21-features/output/12-structured-concurrency.txt b/java21-features/output/12-structured-concurrency.txt
new file mode 100644
index 0000000..4e83aeb
--- /dev/null
+++ b/java21-features/output/12-structured-concurrency.txt
@@ -0,0 +1,3 @@
+$ javac --release 21 --enable-preview src/StructuredConcurrencyPreview.java && java --enable-preview StructuredConcurrencyPreview     (21.0.12.1)
+both subtasks   : ankur / 42
+failure shuts down siblings: java.lang.IllegalStateException: boom
diff --git a/java21-features/output/13-ffm.txt b/java21-features/output/13-ffm.txt
new file mode 100644
index 0000000..fbb5bbb
--- /dev/null
+++ b/java21-features/output/13-ffm.txt
@@ -0,0 +1,2 @@
+$ javac --release 21 --enable-preview src/FfmPreview.java && java --enable-preview --enable-native-access=ALL-UNNAMED FfmPreview     (21.0.12.1)
+strlen("Hello Ankur") = 11
diff --git a/java21-features/output/14-compile-errors.txt b/java21-features/output/14-compile-errors.txt
new file mode 100644
index 0000000..6e44e0f
--- /dev/null
+++ b/java21-features/output/14-compile-errors.txt
@@ -0,0 +1,18 @@
+$ javac  broken/PreviewWithoutFlag.java     (21.0.12.1)
+broken/PreviewWithoutFlag.java:3: error: string templates are a preview feature and are disabled by default.
+    public static void main(String[] args) { String n = "x"; System.out.println(STR."hi \{n}"); }
+                                                                                    ^
+  (use --enable-preview to enable string templates)
+1 error
+
+$ javac  broken/NonExhaustive.java     (21.0.12.1)
+broken/NonExhaustive.java:6: error: the switch expression does not cover all possible input values
+    static String f(S s) { return switch (s) { case A a -> "a"; }; }
+                                  ^
+1 error
+
+$ javac  broken/DominatedCase.java     (21.0.12.1)
+broken/DominatedCase.java:3: error: this case label is dominated by a preceding case label
+    static String f(Object o) { return switch (o) { case CharSequence cs -> "cs"; case String s -> "s"; default -> "d"; }; }
+                                                                                       ^
+1 error
diff --git a/java21-features/run.sh b/java21-features/run.sh
new file mode 100755
index 0000000..0afd8eb
--- /dev/null
+++ b/java21-features/run.sh
@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+# Java 21 features: every demo compiled and run on a real JDK 21; regenerates output/*.txt
+#   JDK21=/path/to/jdk21 ./run.sh
+set -uo pipefail
+unset JAVA_TOOL_OPTIONS
+HERE="$(cd "$(dirname "$0")" && pwd)"
+JDK21="${JDK21:-/opt/jdks/jdk21}"
+OUT="$HERE/output"; mkdir -p "$OUT"; B="$(mktemp -d)"; trap 'rm -rf "$B"' EXIT
+cd "$HERE"
+ver() { "$1/bin/java" -version 2>&1 | sed -n 1p | sed 's/.*"\(.*\)".*/\1/'; }
+# cr FILE CLASS [javac flags...] -- [java flags...]
+cr() { local src="$1" cls="$2"; shift 2; local jf=() rf=(); while [ $# -gt 0 ] && [ "$1" != "--" ]; do jf+=("$1"); shift; done; [ "${1:-}" = "--" ] && shift; rf=("$@")
+  local o; o="$(mktemp -d -p "$B")"
+  echo "\$ javac ${jf[*]:-} $src && java ${rf[*]:-} $cls     ($(ver "$JDK21"))"
+  "$JDK21/bin/javac" "${jf[@]}" -encoding UTF-8 -d "$o" "$src" 2>&1 | grep -v -e '^Note:' ; "$JDK21/bin/java" "${rf[@]}" -cp "$o" "$cls" 2>&1; }
+co() { local src="$1"; shift; local o; o="$(mktemp -d -p "$B")"
+  echo "\$ javac $* $src     ($(ver "$JDK21"))"; local r; r="$("$JDK21/bin/javac" "$@" -encoding UTF-8 -d "$o" "$src" 2>&1 | grep -v -e '^Note:')"; if [ -n "$r" ]; then echo "$r"; else echo "(compiled cleanly)"; fi; }
+PV=(--release 21 --enable-preview)
+cr src/VirtualThreadsDemo.java VirtualThreadsDemo        > "$OUT/01-virtual-threads.txt"
+cr src/RecordPatternsDemo.java RecordPatternsDemo        > "$OUT/02-record-patterns.txt"
+cr src/PatternSwitchDemo.java PatternSwitchDemo          > "$OUT/03-pattern-switch.txt"
+cr src/SequencedCollectionsDemo.java SequencedCollectionsDemo > "$OUT/04-sequenced-collections.txt"
+cr src/KemDemo.java KemDemo                              > "$OUT/05-kem.txt"
+{ cr src/GcNamesDemo.java GcNamesDemo -- -XX:+UseZGC; echo; cr src/GcNamesDemo.java GcNamesDemo -- -XX:+UseZGC -XX:+ZGenerational; } > "$OUT/06-generational-zgc.txt"
+cr src/VectorDemo.java VectorDemo --add-modules jdk.incubator.vector -- --add-modules jdk.incubator.vector > "$OUT/07-vector-api.txt"
+cr src/StringTemplatesPreview.java StringTemplatesPreview "${PV[@]}" -- --enable-preview > "$OUT/08-string-templates.txt"
+cr src/UnnamedPreview.java UnnamedPreview "${PV[@]}" -- --enable-preview > "$OUT/09-unnamed-patterns.txt"
+{ echo "\$ java --enable-preview --source 21 src/UnnamedMainPreview.java     ($(ver "$JDK21"))"; "$JDK21/bin/java" --enable-preview --source 21 src/UnnamedMainPreview.java 2>&1 | grep -v '^Note:'; } > "$OUT/10-unnamed-main.txt"
+cr src/ScopedValuesPreview.java ScopedValuesPreview "${PV[@]}" -- --enable-preview > "$OUT/11-scoped-values.txt"
+cr src/StructuredConcurrencyPreview.java StructuredConcurrencyPreview "${PV[@]}" -- --enable-preview > "$OUT/12-structured-concurrency.txt"
+cr src/FfmPreview.java FfmPreview "${PV[@]}" -- --enable-preview --enable-native-access=ALL-UNNAMED > "$OUT/13-ffm.txt"
+{ co broken/PreviewWithoutFlag.java; echo; co broken/NonExhaustive.java; echo; co broken/DominatedCase.java; } > "$OUT/14-compile-errors.txt"
+exit 0
diff --git a/java21-features/src/FfmPreview.java b/java21-features/src/FfmPreview.java
new file mode 100644
index 0000000..2812b9a
--- /dev/null
+++ b/java21-features/src/FfmPreview.java
@@ -0,0 +1,16 @@
+import java.lang.foreign.*;
+import java.lang.invoke.MethodHandle;
+
+/** JEP 442 (third preview in 21): call C's strlen without JNI. Needs --enable-preview. */
+public class FfmPreview {
+    public static void main(String[] args) throws Throwable {
+        Linker linker = Linker.nativeLinker();
+        MethodHandle strlen = linker.downcallHandle(linker.defaultLookup().find("strlen").orElseThrow(),
+                FunctionDescriptor.of(ValueLayout.JAVA_LONG, ValueLayout.ADDRESS));
+        try (Arena arena = Arena.ofConfined()) {
+            MemorySegment s = arena.allocateUtf8String("Hello Ankur");
+            long len = (long) strlen.invokeExact(s);
+            System.out.println("strlen(\"Hello Ankur\") = " + len);
+        }
+    }
+}
diff --git a/java21-features/src/GcNamesDemo.java b/java21-features/src/GcNamesDemo.java
new file mode 100644
index 0000000..cabf341
--- /dev/null
+++ b/java21-features/src/GcNamesDemo.java
@@ -0,0 +1,8 @@
+import java.lang.management.*;
+
+/** JEP 439 (final): Generational ZGC is opt-in on 21 with -XX:+ZGenerational. Prints the GC beans each mode registers. */
+public class GcNamesDemo {
+    public static void main(String[] args) {
+        for (GarbageCollectorMXBean b : ManagementFactory.getGarbageCollectorMXBeans()) System.out.println("gc bean         : " + b.getName());
+    }
+}
diff --git a/java21-features/src/KemDemo.java b/java21-features/src/KemDemo.java
new file mode 100644
index 0000000..7f68941
--- /dev/null
+++ b/java21-features/src/KemDemo.java
@@ -0,0 +1,20 @@
+import javax.crypto.*;
+import java.security.*;
+import java.util.Arrays;
+
+/** JEP 452 (final): Key Encapsulation Mechanism API, with the DHKEM implementation that ships in 21. */
+public class KemDemo {
+    public static void main(String[] args) throws Exception {
+        KeyPairGenerator g = KeyPairGenerator.getInstance("X25519");
+        KeyPair kp = g.generateKeyPair();
+        KEM kem = KEM.getInstance("DHKEM");
+        KEM.Encapsulator enc = kem.newEncapsulator(kp.getPublic());
+        KEM.Encapsulated e = enc.encapsulate();
+        SecretKey sender = e.key();
+        SecretKey receiver = kem.newDecapsulator(kp.getPrivate()).decapsulate(e.encapsulation());
+        System.out.println("algorithm       : " + kem.getAlgorithm());
+        System.out.println("secrets equal   : " + Arrays.equals(sender.getEncoded(), receiver.getEncoded()));
+        System.out.println("secret length   : " + sender.getEncoded().length + " bytes");
+        System.out.println("ciphertext length: " + e.encapsulation().length + " bytes");
+    }
+}
diff --git a/java21-features/src/PatternSwitchDemo.java b/java21-features/src/PatternSwitchDemo.java
new file mode 100644
index 0000000..d1d329e
--- /dev/null
+++ b/java21-features/src/PatternSwitchDemo.java
@@ -0,0 +1,29 @@
+/** JEP 441 (final): patterns in switch, guards with `when`, case null, and exhaustiveness over a sealed type. */
+public class PatternSwitchDemo {
+    sealed interface Shape permits Circle, Square, Rect {}
+    record Circle(double r) implements Shape {}
+    record Square(double side) implements Shape {}
+    record Rect(double w, double h) implements Shape {}
+
+    static String size(Shape s) {
+        return switch (s) {                                   // no default: the compiler checks all three cases
+            case Circle c when c.r() > 10 -> "big circle";
+            case Circle c -> "circle";
+            case Square q -> "square " + q.side();
+            case Rect(double w, double h) -> "rect " + w + "x" + h;
+        };
+    }
+    static String any(Object o) {
+        return switch (o) {
+            case null -> "null handled in the switch";
+            case Integer i when i > 100 -> "large int";
+            case Integer i -> "int";
+            case String str -> "string of " + str.length();
+            default -> "other";
+        };
+    }
+    public static void main(String[] args) {
+        System.out.println(size(new Circle(11)) + " | " + size(new Circle(1)) + " | " + size(new Square(2)) + " | " + size(new Rect(2, 3)));
+        System.out.println(any(null) + " | " + any(500) + " | " + any(5) + " | " + any("abcd") + " | " + any(2.0));
+    }
+}
diff --git a/java21-features/src/RecordPatternsDemo.java b/java21-features/src/RecordPatternsDemo.java
new file mode 100644
index 0000000..e9d12b2
--- /dev/null
+++ b/java21-features/src/RecordPatternsDemo.java
@@ -0,0 +1,20 @@
+/** JEP 440 (final): deconstruct records in instanceof and switch, nested. */
+public class RecordPatternsDemo {
+    record Point(int x, int y) {}
+    record Line(Point from, Point to) {}
+    record Box<T>(T content) {}
+
+    static String describe(Object o) {
+        if (o instanceof Line(Point(var x1, var y1), Point(var x2, var y2)))
+            return "line from (" + x1 + "," + y1 + ") to (" + x2 + "," + y2 + ") length^2=" + ((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
+        if (o instanceof Box<?>(String s)) return "box of String " + s;
+        if (o instanceof Box<?>(Integer i)) return "box of Integer " + i;
+        return "no match";
+    }
+    public static void main(String[] args) {
+        System.out.println(describe(new Line(new Point(0, 0), new Point(3, 4))));
+        System.out.println(describe(new Box<>("hi")));
+        System.out.println(describe(new Box<>(7)));
+        System.out.println(describe(new Box<>(2.5)));
+    }
+}
diff --git a/java21-features/src/ScopedValuesPreview.java b/java21-features/src/ScopedValuesPreview.java
new file mode 100644
index 0000000..9495812
--- /dev/null
+++ b/java21-features/src/ScopedValuesPreview.java
@@ -0,0 +1,9 @@
+/** JEP 446 (preview in 21): ScopedValue binds a value for the dynamic extent of a call. Needs --enable-preview. */
+public class ScopedValuesPreview {
+    static final ScopedValue<String> USER = ScopedValue.newInstance();
+    static void handler() { System.out.println("inside handler  : user=" + USER.get()); }
+    public static void main(String[] args) {
+        ScopedValue.where(USER, "ankur").run(ScopedValuesPreview::handler);
+        System.out.println("outside         : bound=" + USER.isBound());
+    }
+}
diff --git a/java21-features/src/SequencedCollectionsDemo.java b/java21-features/src/SequencedCollectionsDemo.java
new file mode 100644
index 0000000..be48448
--- /dev/null
+++ b/java21-features/src/SequencedCollectionsDemo.java
@@ -0,0 +1,29 @@
+import java.util.*;
+
+/** JEP 431 (final): SequencedCollection, SequencedSet, SequencedMap. */
+public class SequencedCollectionsDemo {
+    public static void main(String[] args) {
+        List<String> list = new ArrayList<>(List.of("a", "b", "c"));
+        System.out.println("getFirst/getLast: " + list.getFirst() + " " + list.getLast());
+        System.out.println("reversed view   : " + list.reversed());
+        list.addFirst("z"); list.removeLast();
+        System.out.println("addFirst+removeLast: " + list);
+
+        LinkedHashSet<Integer> set = new LinkedHashSet<>(List.of(1, 2, 3));
+        System.out.println("LinkedHashSet reversed: " + set.reversed());
+
+        LinkedHashMap<String, Integer> map = new LinkedHashMap<>();
+        map.put("x", 1); map.put("y", 2); map.put("z", 3);
+        System.out.println("firstEntry/lastEntry : " + map.firstEntry() + " " + map.lastEntry());
+        map.putFirst("w", 0);
+        System.out.println("putFirst        : " + map);
+        System.out.println("reversed map    : " + map.reversed());
+
+        // reversed() is a view, not a copy
+        List<String> src = new ArrayList<>(List.of("1", "2")); List<String> rev = src.reversed(); src.add("3");
+        System.out.println("view sees add   : " + rev);
+
+        try { List.of(1, 2).addFirst(0); } catch (UnsupportedOperationException e) { System.out.println("immutable list : UnsupportedOperationException"); }
+        try { new HashSet<>(List.of(1)).getClass().getMethod("getFirst"); } catch (NoSuchMethodException e) { System.out.println("HashSet         : no getFirst (unordered)"); }
+    }
+}
diff --git a/java21-features/src/StringTemplatesPreview.java b/java21-features/src/StringTemplatesPreview.java
new file mode 100644
index 0000000..a99850d
--- /dev/null
+++ b/java21-features/src/StringTemplatesPreview.java
@@ -0,0 +1,7 @@
+/** JEP 430 (preview in 21, withdrawn in later releases). Needs --enable-preview. */
+public class StringTemplatesPreview {
+    public static void main(String[] args) {
+        String name = "Ankur"; int a = 3, b = 4;
+        System.out.println(STR."Hello \{name}, \{a} + \{b} = \{a + b}");
+    }
+}
diff --git a/java21-features/src/StructuredConcurrencyPreview.java b/java21-features/src/StructuredConcurrencyPreview.java
new file mode 100644
index 0000000..667ecc4
--- /dev/null
+++ b/java21-features/src/StructuredConcurrencyPreview.java
@@ -0,0 +1,20 @@
+import java.util.concurrent.StructuredTaskScope;
+
+/** JEP 453 (preview in 21): fork subtasks, join, and let the scope own their lifetime. Needs --enable-preview. */
+public class StructuredConcurrencyPreview {
+    public static void main(String[] args) throws Exception {
+        try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
+            var user = scope.fork(() -> { Thread.sleep(50); return "ankur"; });
+            var order = scope.fork(() -> { Thread.sleep(80); return 42; });
+            scope.join().throwIfFailed();
+            System.out.println("both subtasks   : " + user.get() + " / " + order.get());
+        }
+        try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
+            scope.fork(() -> { throw new IllegalStateException("boom"); });
+            scope.fork(() -> { Thread.sleep(5_000); return "never"; });
+            scope.join().throwIfFailed();
+        } catch (java.util.concurrent.ExecutionException e) {
+            System.out.println("failure shuts down siblings: " + e.getCause());
+        }
+    }
+}
diff --git a/java21-features/src/UnnamedMainPreview.java b/java21-features/src/UnnamedMainPreview.java
new file mode 100644
index 0000000..5fcde1a
--- /dev/null
+++ b/java21-features/src/UnnamedMainPreview.java
@@ -0,0 +1,4 @@
+/** JEP 445 (preview in 21): an unnamed class with an instance main. Needs --enable-preview --source 21. */
+void main() {
+    System.out.println("no class, no static, no String[] args");
+}
diff --git a/java21-features/src/UnnamedPreview.java b/java21-features/src/UnnamedPreview.java
new file mode 100644
index 0000000..f1da4dd
--- /dev/null
+++ b/java21-features/src/UnnamedPreview.java
@@ -0,0 +1,12 @@
+/** JEP 443 (preview in 21): unnamed patterns and variables, `_`. Needs --enable-preview. */
+public class UnnamedPreview {
+    record Point(int x, int y) {}
+    public static void main(String[] args) {
+        Object o = new Point(5, 9);
+        if (o instanceof Point(var x, _)) System.out.println("x only         : " + x);
+        int total = 0;
+        for (var _ : java.util.List.of("a", "b", "c")) total++;
+        System.out.println("loop count      : " + total);
+        try { Integer.parseInt("zz"); } catch (NumberFormatException _) { System.out.println("caught, name not needed"); }
+    }
+}
diff --git a/java21-features/src/VectorDemo.java b/java21-features/src/VectorDemo.java
new file mode 100644
index 0000000..fdee48d
--- /dev/null
+++ b/java21-features/src/VectorDemo.java
@@ -0,0 +1,16 @@
+import jdk.incubator.vector.*;
+
+/** JEP 448 (sixth incubator): needs --add-modules jdk.incubator.vector. Result must equal the scalar loop. */
+public class VectorDemo {
+    static final VectorSpecies<Integer> S = IntVector.SPECIES_PREFERRED;
+    public static void main(String[] args) {
+        int n = 1000; int[] a = new int[n], b = new int[n], c = new int[n], d = new int[n];
+        for (int i = 0; i < n; i++) { a[i] = i; b[i] = 2 * i; }
+        int i = 0;
+        for (; i < S.loopBound(n); i += S.length()) IntVector.fromArray(S, a, i).add(IntVector.fromArray(S, b, i)).intoArray(c, i);
+        for (; i < n; i++) c[i] = a[i] + b[i];
+        for (int k = 0; k < n; k++) d[k] = a[k] + b[k];
+        System.out.println("vector == scalar: " + java.util.Arrays.equals(c, d));
+        System.out.println("lanes >= 2      : " + (S.length() >= 2));
+    }
+}
diff --git a/java21-features/src/VirtualThreadsDemo.java b/java21-features/src/VirtualThreadsDemo.java
new file mode 100644
index 0000000..5207f31
--- /dev/null
+++ b/java21-features/src/VirtualThreadsDemo.java
@@ -0,0 +1,22 @@
+import java.time.Duration;
+import java.util.concurrent.*;
+import java.util.concurrent.atomic.AtomicInteger;
+
+/** JEP 444 (final): 10,000 blocking tasks on virtual threads. Timing is machine dependent, so only counts are asserted. */
+public class VirtualThreadsDemo {
+    public static void main(String[] args) throws Exception {
+        AtomicInteger done = new AtomicInteger();
+        long t0 = System.nanoTime();
+        try (ExecutorService ex = Executors.newVirtualThreadPerTaskExecutor()) {
+            for (int i = 0; i < 10_000; i++) ex.submit(() -> { Thread.sleep(Duration.ofSeconds(1)); done.incrementAndGet(); return null; });
+        }
+        long ms = (System.nanoTime() - t0) / 1_000_000;
+        System.out.println("tasks completed : " + done.get());
+        System.out.println("finished in < 5s: " + (ms < 5_000) + "   (10,000 x 1s sleeps)");
+
+        Thread v = Thread.ofVirtual().name("demo-vt").start(() -> System.out.println("isVirtual       : " + Thread.currentThread().isVirtual() + ", daemon=" + Thread.currentThread().isDaemon()));
+        v.join();
+        Thread p = Thread.ofPlatform().name("demo-pt").start(() -> System.out.println("platform isVirtual: " + Thread.currentThread().isVirtual()));
+        p.join();
+    }
+}