With JDK-8330582, the JVM starts to enforce new field modifiers rules from JEP 401, notably:
"A field that has set ACC_STRICT must also have set ACC_FINAL."
and
"Each field of a value class must have exactly one of its ACC_STATIC or ACC_STRICT flags set.".

Enforcing those rules shows an issue with javac: when generating final synthetic fields in value classes, the ACC_STRICT flag is not set.

Reproducer:

public class NestedTest {
    value class MyValue {
int i = 0;

public String toString() {
return "MyValue("+i+","+outerInt+")";
}
    }

    int outerInt = 42;
    MyValue v = new MyValue();

    public static void main(String[] args) {
NestedTest nt = new NestedTest();
    }
}

Error reported by the JVM (with JDK-8330582 changes in):

Exception in thread "main" java.lang.ClassFormatError: Illegal field modifiers in class NestedTest$MyValue: 0x1010
at java.base/java.lang.ClassLoader.defineClass1(Native Method)
at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1023)
at java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:150)
at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:862)
at java.base/jdk.internal.loader.BuiltinClassLoader.findClassOnClassPathOrNull(BuiltinClassLoader.java:760)
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClassOrNull(BuiltinClassLoader.java:681)
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:639)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:525)
at NestedTest.<init>(NestedTest.java:11)
at NestedTest.main(NestedTest.java:14)


Decompiling the value class shows the illegal field modifiers set for field this$0 :

Classfile [...]/NestedTest$MyValue.class
  Last modified Apr 18, 2024; size 965 bytes
  SHA-256 checksum e3a71b30c8be9b0529a3297b2bc499abf9a188455a5c4a5463e8217e89520040
  Compiled from "NestedTest.java"
final value class NestedTest$MyValue
  minor version: 65535
  major version: 66
  flags: (0x0010) ACC_FINAL
  this_class: #2 // NestedTest$MyValue
  super_class: #12 // java/lang/Object
  interfaces: 0, fields: 2, methods: 2, attributes: 4
Constant pool:
   #1 = Fieldref #2.#3 // NestedTest$MyValue.this$0:LNestedTest;
   #2 = Class #4 // NestedTest$MyValue
   #3 = NameAndType #5:#6 // this$0:LNestedTest;
   #4 = Utf8 NestedTest$MyValue
   #5 = Utf8 this$0
   #6 = Utf8 LNestedTest;
   #7 = Fieldref #2.#8 // NestedTest$MyValue.i:I
   #8 = NameAndType #9:#10 // i:I
   #9 = Utf8 i
  #10 = Utf8 I
  #11 = Methodref #12.#13 // java/lang/Object."<init>":()V
  #12 = Class #14 // java/lang/Object
  #13 = NameAndType #15:#16 // "<init>":()V
  #14 = Utf8 java/lang/Object
  #15 = Utf8 <init>
  #16 = Utf8 ()V
  #17 = Fieldref #18.#19 // NestedTest.outerInt:I
  #18 = Class #20 // NestedTest
  #19 = NameAndType #21:#10 // outerInt:I
  #20 = Utf8 NestedTest
  #21 = Utf8 outerInt
  #22 = InvokeDynamic #0:#23 // #0:makeConcatWithConstants:(I)Ljava/lang/String;
  #23 = NameAndType #24:#25 // makeConcatWithConstants:(I)Ljava/lang/String;
  #24 = Utf8 makeConcatWithConstants
  #25 = Utf8 (I)Ljava/lang/String;
  #26 = Utf8 ConstantValue
  #27 = Integer 0
  #28 = Utf8 (LNestedTest;)V
  #29 = Utf8 Code
  #30 = Utf8 LineNumberTable
  #31 = Utf8 MethodParameters
  #32 = Utf8 toString
  #33 = Utf8 ()Ljava/lang/String;
  #34 = Utf8 SourceFile
  #35 = Utf8 NestedTest.java
  #36 = Utf8 NestHost
  #37 = Utf8 BootstrapMethods
  #38 = String #39 // MyValue(0,\u0001)
  #39 = Utf8 MyValue(0,\u0001)
  #40 = MethodHandle 6:#41 // REF_invokeStatic java/lang/invoke/StringConcatFactory.makeConcatWithConstants:(Ljava/lang/invoke/MethodHandles$Looku
p;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/invoke/CallSite;
  #41 = Methodref #42.#43 // java/lang/invoke/StringConcatFactory.makeConcatWithConstants:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/Stri
ng;Ljava/lang/invoke/MethodType;Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/invoke/CallSite;
  #42 = Class #44 // java/lang/invoke/StringConcatFactory
  #43 = NameAndType #24:#45 // makeConcatWithConstants:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava
/lang/String;[Ljava/lang/Object;)Ljava/lang/invoke/CallSite;
  #44 = Utf8 java/lang/invoke/StringConcatFactory
  #45 = Utf8 (Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/String;[Ljava/lang/Object;)Ljava/lan
g/invoke/CallSite;
  #46 = Utf8 InnerClasses
  #47 = Utf8 MyValue
  #48 = Class #49 // java/lang/invoke/MethodHandles$Lookup
  #49 = Utf8 java/lang/invoke/MethodHandles$Lookup
  #50 = Class #51 // java/lang/invoke/MethodHandles
  #51 = Utf8 java/lang/invoke/MethodHandles
  #52 = Utf8 Lookup
{
  final strictfp int i;
    descriptor: I
    flags: (0x0810) ACC_FINAL, ACC_STRICT
    ConstantValue: int 0

  final NestedTest this$0;
    descriptor: LNestedTest;
    flags: (0x1010) ACC_FINAL, ACC_SYNTHETIC

  NestedTest$MyValue(NestedTest);
    descriptor: (LNestedTest;)V
    flags: (0x0000)
    Code:
      stack=2, locals=2, args_size=2
         0: aload_0
         1: aload_1
         2: putfield #1 // Field this$0:LNestedTest;
         5: aload_0
         6: iconst_0
         7: putfield #7 // Field i:I
        10: aload_0
        11: invokespecial #11 // Method java/lang/Object."<init>":()V
        14: return
      LineNumberTable:
        line 2: 0
        line 3: 5
        line 2: 10
    MethodParameters:
      Name Flags
      <no name> final mandated

  public java.lang.String toString();
    descriptor: ()Ljava/lang/String;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: getfield #1 // Field this$0:LNestedTest;
         4: getfield #17 // Field NestedTest.outerInt:I
         7: invokedynamic #22, 0 // InvokeDynamic #0:makeConcatWithConstants:(I)Ljava/lang/String;
        12: areturn
      LineNumberTable:
        line 6: 0
}
SourceFile: "NestedTest.java"
NestHost: class NestedTest
BootstrapMethods:
  0: #40 REF_invokeStatic java/lang/invoke/StringConcatFactory.makeConcatWithConstants:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invok
e/MethodType;Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/invoke/CallSite;
    Method arguments:
      #38 MyValue(0,\u0001)
InnerClasses:
  final #47= #2 of #18; // MyValue=class NestedTest$MyValue of class NestedTest
  public static final #52= #48 of #50; // Lookup=class java/lang/invoke/MethodHandles$Lookup of class java/lang/invoke/MethodHandles


Another minor issue, for field 'i', javap prints " final strictfp int i;" when it should print " final strict int i;".