diff --git a/src/main/java/com/android/tools/r8/L8Command.java b/src/main/java/com/android/tools/r8/L8Command.java
index 339e80b..0bd58e6 100644
--- a/src/main/java/com/android/tools/r8/L8Command.java
+++ b/src/main/java/com/android/tools/r8/L8Command.java
@@ -387,6 +387,7 @@
         R8Command.Builder r8Builder =
             R8Command.builder(getReporter())
                 .addProgramResourceProvider((ProgramResourceProvider) l8CfConsumer)
+                .setEnableEmptyMemberRulesToDefaultInitRuleConversion(false)
                 .setSynthesizedClassesPrefix(
                     desugaredLibrarySpecification.getSynthesizedLibraryClassesPackagePrefix())
                 .setMinApiLevel(getMinApiLevel())
diff --git a/src/main/java/com/android/tools/r8/errors/EmptyMemberRulesToDefaultInitRuleConversionDiagnostic.java b/src/main/java/com/android/tools/r8/errors/EmptyMemberRulesToDefaultInitRuleConversionDiagnostic.java
new file mode 100644
index 0000000..9a441ce
--- /dev/null
+++ b/src/main/java/com/android/tools/r8/errors/EmptyMemberRulesToDefaultInitRuleConversionDiagnostic.java
@@ -0,0 +1,52 @@
+// Copyright (c) 2024, the R8 project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+package com.android.tools.r8.errors;
+
+import com.android.tools.r8.Diagnostic;
+import com.android.tools.r8.keepanno.annotations.KeepForApi;
+import com.android.tools.r8.origin.Origin;
+import com.android.tools.r8.position.Position;
+import com.android.tools.r8.shaking.ProguardConfigurationRule;
+import com.android.tools.r8.utils.StringUtils;
+
+@KeepForApi
+public class EmptyMemberRulesToDefaultInitRuleConversionDiagnostic implements Diagnostic {
+
+  private final ProguardConfigurationRule rule;
+
+  EmptyMemberRulesToDefaultInitRuleConversionDiagnostic(ProguardConfigurationRule rule) {
+    this.rule = rule;
+  }
+
+  @Override
+  public Origin getOrigin() {
+    return rule.getOrigin();
+  }
+
+  @Override
+  public Position getPosition() {
+    return rule.getPosition();
+  }
+
+  @Override
+  public String getDiagnosticMessage() {
+    // TODO(b/356350498): Explain how to opt-in to the new behavior when this is implemented in AGP.
+    return StringUtils.joinLines(
+        "The current version of R8 implicitly keeps the default constructor for Proguard"
+            + " configuration rules that have no member pattern. If the following rule should"
+            + " continue to keep the default constructor in the next major version of R8, then it"
+            + " must be augmented with the member pattern `{ void <init>(); }` to explicitly keep"
+            + " the default constructor:",
+        rule.toString());
+  }
+
+  // Non-kept factory to avoid that the constructor of the diagnostic is public API.
+  public static class Factory {
+
+    public static EmptyMemberRulesToDefaultInitRuleConversionDiagnostic create(
+        ProguardConfigurationRule rule) {
+      return new EmptyMemberRulesToDefaultInitRuleConversionDiagnostic(rule);
+    }
+  }
+}
diff --git a/src/main/java/com/android/tools/r8/shaking/ProguardConfigurationParser.java b/src/main/java/com/android/tools/r8/shaking/ProguardConfigurationParser.java
index fc42207..f511bee 100644
--- a/src/main/java/com/android/tools/r8/shaking/ProguardConfigurationParser.java
+++ b/src/main/java/com/android/tools/r8/shaking/ProguardConfigurationParser.java
@@ -10,6 +10,7 @@
 import com.android.tools.r8.InputDependencyGraphConsumer;
 import com.android.tools.r8.Version;
 import com.android.tools.r8.dex.Constants;
+import com.android.tools.r8.errors.EmptyMemberRulesToDefaultInitRuleConversionDiagnostic;
 import com.android.tools.r8.graph.DexItemFactory;
 import com.android.tools.r8.graph.DexString;
 import com.android.tools.r8.graph.DexType;
@@ -32,6 +33,7 @@
 import com.android.tools.r8.utils.ThrowingAction;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Iterables;
+import com.google.common.collect.Lists;
 import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.IOException;
@@ -127,6 +129,7 @@
         dexItemFactory,
         reporter,
         ProguardConfigurationParserOptions.builder()
+            .setEnableEmptyMemberRulesToDefaultInitRuleConversion(false)
             .setEnableExperimentalCheckEnumUnboxed(false)
             .setEnableExperimentalConvertCheckNotNull(false)
             .setEnableExperimentalWhyAreYouNotInlining(false)
@@ -846,28 +849,31 @@
           .setStart(start);
       parseRuleTypeAndModifiers(keepRuleBuilder);
       parseClassSpec(keepRuleBuilder);
-      if (options.isEmptyMemberRulesToDefaultInitRuleConversionEnabled(configurationBuilder)) {
-        if (keepRuleBuilder.getMemberRules().isEmpty()
-            && keepRuleBuilder.getKeepRuleType()
-                != ProguardKeepRuleType.KEEP_CLASSES_WITH_MEMBERS) {
-          // If there are no member rules, a default rule for the parameterless constructor applies
-          // in compatibility mode.
-          keepRuleBuilder
-              .getMemberRules()
-              .add(
-                  ProguardMemberRule.builder()
-                      .setName(
-                          IdentifierPatternWithWildcards.withoutWildcards(
-                              Constants.INSTANCE_INITIALIZER_NAME))
-                      .setRuleType(ProguardMemberType.INIT)
-                      .setArguments(Collections.emptyList())
-                      .build());
-        }
-      }
       Position end = getPosition();
-      keepRuleBuilder.setSource(getSourceSnippet(contents, start, end));
-      keepRuleBuilder.setEnd(end);
-      return keepRuleBuilder.build();
+      ProguardKeepRule rule =
+          keepRuleBuilder.setSource(getSourceSnippet(contents, start, end)).setEnd(end).build();
+      if (options.isEmptyMemberRulesToDefaultInitRuleConversionEnabled(configurationBuilder)
+          && rule.getMemberRules().isEmpty()
+          && rule.getType() != ProguardKeepRuleType.KEEP_CLASSES_WITH_MEMBERS) {
+        // If there are no member rules, a default rule for the parameterless constructor applies
+        // in compatibility mode.
+        if (options.isEmptyMemberRulesToDefaultInitRuleConversionWarningsEnabled(
+            configurationBuilder)) {
+          reporter.warning(
+              EmptyMemberRulesToDefaultInitRuleConversionDiagnostic.Factory.create(rule));
+        }
+        List<ProguardMemberRule> memberRules =
+            Lists.newArrayList(
+                ProguardMemberRule.builder()
+                    .setName(
+                        IdentifierPatternWithWildcards.withoutWildcards(
+                            Constants.INSTANCE_INITIALIZER_NAME))
+                    .setRuleType(ProguardMemberType.INIT)
+                    .setArguments(Collections.emptyList())
+                    .build());
+        rule = keepRuleBuilder.setMemberRules(memberRules).build();
+      }
+      return rule;
     }
 
     @SuppressWarnings("NonCanonicalType")
diff --git a/src/main/java/com/android/tools/r8/shaking/ProguardConfigurationParserOptions.java b/src/main/java/com/android/tools/r8/shaking/ProguardConfigurationParserOptions.java
index 157be68..07bea60 100644
--- a/src/main/java/com/android/tools/r8/shaking/ProguardConfigurationParserOptions.java
+++ b/src/main/java/com/android/tools/r8/shaking/ProguardConfigurationParserOptions.java
@@ -6,16 +6,18 @@
 
 import static com.android.tools.r8.utils.SystemPropertyUtils.parseSystemPropertyOrDefault;
 
+import com.android.tools.r8.utils.OptionalBool;
+
 public class ProguardConfigurationParserOptions {
 
-  private final boolean enableEmptyMemberRulesToDefaultInitRuleConversion;
+  private final OptionalBool enableEmptyMemberRulesToDefaultInitRuleConversion;
   private final boolean enableExperimentalCheckEnumUnboxed;
   private final boolean enableExperimentalConvertCheckNotNull;
   private final boolean enableExperimentalWhyAreYouNotInlining;
   private final boolean enableTestingOptions;
 
   ProguardConfigurationParserOptions(
-      boolean enableEmptyMemberRulesToDefaultInitRuleConversion,
+      OptionalBool enableEmptyMemberRulesToDefaultInitRuleConversion,
       boolean enableExperimentalCheckEnumUnboxed,
       boolean enableExperimentalConvertCheckNotNull,
       boolean enableExperimentalWhyAreYouNotInlining,
@@ -34,8 +36,16 @@
 
   public boolean isEmptyMemberRulesToDefaultInitRuleConversionEnabled(
       ProguardConfiguration.Builder configurationBuilder) {
-    return enableEmptyMemberRulesToDefaultInitRuleConversion
-        || configurationBuilder.isForceProguardCompatibility();
+    // TODO(b/356344563): Disable in full mode in the next major version.
+    return configurationBuilder.isForceProguardCompatibility()
+        || enableEmptyMemberRulesToDefaultInitRuleConversion.getOrDefault(true);
+  }
+
+  public boolean isEmptyMemberRulesToDefaultInitRuleConversionWarningsEnabled(
+      ProguardConfiguration.Builder configurationBuilder) {
+    assert isEmptyMemberRulesToDefaultInitRuleConversionEnabled(configurationBuilder);
+    return !configurationBuilder.isForceProguardCompatibility()
+        && enableEmptyMemberRulesToDefaultInitRuleConversion.isUnknown();
   }
 
   public boolean isExperimentalCheckEnumUnboxedEnabled() {
@@ -56,7 +66,7 @@
 
   public static class Builder {
 
-    private boolean enableEmptyMemberRulesToDefaultInitRuleConversion;
+    private OptionalBool enableEmptyMemberRulesToDefaultInitRuleConversion = OptionalBool.UNKNOWN;
     private boolean enableExperimentalCheckEnumUnboxed;
     private boolean enableExperimentalConvertCheckNotNull;
     private boolean enableExperimentalWhyAreYouNotInlining;
@@ -65,7 +75,8 @@
     public Builder readEnvironment() {
       enableEmptyMemberRulesToDefaultInitRuleConversion =
           parseSystemPropertyOrDefault(
-              "com.android.tools.r8.enableEmptyMemberRulesToDefaultInitRuleConversion", false);
+              "com.android.tools.r8.enableEmptyMemberRulesToDefaultInitRuleConversion",
+              OptionalBool.UNKNOWN);
       enableExperimentalCheckEnumUnboxed =
           parseSystemPropertyOrDefault(
               "com.android.tools.r8.experimental.enablecheckenumunboxed", false);
@@ -83,7 +94,7 @@
     public Builder setEnableEmptyMemberRulesToDefaultInitRuleConversion(
         boolean enableEmptyMemberRulesToDefaultInitRuleConversion) {
       this.enableEmptyMemberRulesToDefaultInitRuleConversion =
-          enableEmptyMemberRulesToDefaultInitRuleConversion;
+          OptionalBool.of(enableEmptyMemberRulesToDefaultInitRuleConversion);
       return this;
     }
 
diff --git a/src/main/java/com/android/tools/r8/utils/OptionalBool.java b/src/main/java/com/android/tools/r8/utils/OptionalBool.java
index 06cd098..b7c0708 100644
--- a/src/main/java/com/android/tools/r8/utils/OptionalBool.java
+++ b/src/main/java/com/android/tools/r8/utils/OptionalBool.java
@@ -58,6 +58,11 @@
       new OptionalBool() {
 
         @Override
+        public boolean getOrDefault(boolean defaultValue) {
+          return defaultValue;
+        }
+
+        @Override
         public boolean isUnknown() {
           return true;
         }
@@ -93,6 +98,10 @@
     return this;
   }
 
+  public boolean getOrDefault(boolean defaultValue) {
+    return toBoolean();
+  }
+
   public abstract boolean toBoolean();
 
   @Override
diff --git a/src/main/java/com/android/tools/r8/utils/SystemPropertyUtils.java b/src/main/java/com/android/tools/r8/utils/SystemPropertyUtils.java
index 57cb56d..33dffa1 100644
--- a/src/main/java/com/android/tools/r8/utils/SystemPropertyUtils.java
+++ b/src/main/java/com/android/tools/r8/utils/SystemPropertyUtils.java
@@ -7,6 +7,8 @@
 import static com.google.common.base.Predicates.alwaysTrue;
 
 import com.android.tools.r8.Version;
+import com.android.tools.r8.errors.Unreachable;
+import java.util.function.BooleanSupplier;
 import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.function.Supplier;
@@ -59,19 +61,34 @@
 
   public static boolean parseSystemPropertyOrDefault(String propertyName, boolean defaultValue) {
     return internalParseSystemPropertyForDevelopmentOrDefault(
-        propertyName, System.getProperty(propertyName), defaultValue);
+        propertyName, System.getProperty(propertyName), () -> defaultValue);
+  }
+
+  public static OptionalBool parseSystemPropertyOrDefault(
+      String propertyName, OptionalBool defaultValue) {
+    if (System.getProperty(propertyName) == null) {
+      return defaultValue;
+    }
+    boolean value =
+        internalParseSystemPropertyForDevelopmentOrDefault(
+            propertyName,
+            System.getProperty(propertyName),
+            () -> {
+              throw new Unreachable();
+            });
+    return OptionalBool.of(value);
   }
 
   public static boolean parseSystemPropertyForDevelopmentOrDefault(
       String propertyName, boolean defaultValue) {
     return internalParseSystemPropertyForDevelopmentOrDefault(
-        propertyName, getSystemPropertyForDevelopment(propertyName), defaultValue);
+        propertyName, getSystemPropertyForDevelopment(propertyName), () -> defaultValue);
   }
 
   private static boolean internalParseSystemPropertyForDevelopmentOrDefault(
-      String propertyName, String propertyValue, boolean defaultValue) {
+      String propertyName, String propertyValue, BooleanSupplier defaultValue) {
     if (propertyValue == null) {
-      return defaultValue;
+      return defaultValue.getAsBoolean();
     }
     if (StringUtils.isFalsy(propertyValue)) {
       return false;
diff --git a/src/test/java/com/android/tools/r8/compilerapi/diagnostics/ProguardKeepRuleDiagnosticsApiTest.java b/src/test/java/com/android/tools/r8/compilerapi/diagnostics/ProguardKeepRuleDiagnosticsApiTest.java
index fedb449..e4ed3bb 100644
--- a/src/test/java/com/android/tools/r8/compilerapi/diagnostics/ProguardKeepRuleDiagnosticsApiTest.java
+++ b/src/test/java/com/android/tools/r8/compilerapi/diagnostics/ProguardKeepRuleDiagnosticsApiTest.java
@@ -98,6 +98,7 @@
               .addProguardConfiguration(
                   Collections.singletonList("-keep class NotPresent {}"), Origin.unknown())
               .addLibraryFiles(getJava8RuntimeJar())
+              .setEnableEmptyMemberRulesToDefaultInitRuleConversion(false)
               .setProgramConsumer(DexIndexedConsumer.emptyConsumer())
               .setMinApiLevel(1)
               .build());
diff --git a/src/test/java/com/android/tools/r8/shaking/EmptyMemberRulesToDefaultInitRuleConversionTest.java b/src/test/java/com/android/tools/r8/shaking/EmptyMemberRulesToDefaultInitRuleConversionTest.java
index bdb0a85..564eac9 100644
--- a/src/test/java/com/android/tools/r8/shaking/EmptyMemberRulesToDefaultInitRuleConversionTest.java
+++ b/src/test/java/com/android/tools/r8/shaking/EmptyMemberRulesToDefaultInitRuleConversionTest.java
@@ -3,13 +3,23 @@
 // BSD-style license that can be found in the LICENSE file.
 package com.android.tools.r8.shaking;
 
+import static com.android.tools.r8.DiagnosticsMatcher.diagnosticMessage;
+import static com.android.tools.r8.DiagnosticsMatcher.diagnosticType;
 import static com.android.tools.r8.utils.codeinspector.Matchers.isPresent;
 import static com.android.tools.r8.utils.codeinspector.Matchers.isPresentIf;
+import static org.hamcrest.CoreMatchers.allOf;
+import static org.hamcrest.CoreMatchers.equalTo;
 import static org.hamcrest.MatcherAssert.assertThat;
+import static org.junit.Assume.assumeTrue;
 
+import com.android.tools.r8.R8CompatTestBuilder;
+import com.android.tools.r8.R8TestBuilder;
 import com.android.tools.r8.TestBase;
 import com.android.tools.r8.TestParameters;
+import com.android.tools.r8.ThrowableConsumer;
+import com.android.tools.r8.errors.EmptyMemberRulesToDefaultInitRuleConversionDiagnostic;
 import com.android.tools.r8.utils.BooleanUtils;
+import com.android.tools.r8.utils.StringUtils;
 import java.util.List;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -34,19 +44,63 @@
   }
 
   @Test
-  public void testCompat() throws Exception {
+  public void testCompatDefault() throws Exception {
+    assumeTrue(enableEmptyMemberRulesToDefaultInitRuleConversion);
+    testCompat(R8TestBuilder::clearEnableEmptyMemberRulesToDefaultInitRuleConversion);
+  }
+
+  @Test
+  public void testCompatExplicit() throws Exception {
+    testCompat(
+        testBuilder ->
+            testBuilder.enableEmptyMemberRulesToDefaultInitRuleConversion(
+                enableEmptyMemberRulesToDefaultInitRuleConversion));
+  }
+
+  private void testCompat(ThrowableConsumer<? super R8CompatTestBuilder> configuration)
+      throws Exception {
     testForR8Compat(parameters.getBackend())
         .addInnerClasses(getClass())
         .addKeepClassRules(Main.class)
-        .enableEmptyMemberRulesToDefaultInitRuleConversion(
-            enableEmptyMemberRulesToDefaultInitRuleConversion)
+        .apply(configuration)
         .setMinApi(parameters)
         .compile()
         .inspect(inspector -> assertThat(inspector.clazz(Main.class).init(), isPresent()));
   }
 
   @Test
-  public void testFull() throws Exception {
+  public void testFullDefault() throws Exception {
+    assumeTrue(enableEmptyMemberRulesToDefaultInitRuleConversion);
+    testForR8(parameters.getBackend())
+        .addInnerClasses(getClass())
+        .addKeepClassRules(Main.class)
+        .allowDiagnosticWarningMessages()
+        .clearEnableEmptyMemberRulesToDefaultInitRuleConversion()
+        .setMinApi(parameters)
+        .compileWithExpectedDiagnostics(
+            diagnostics ->
+                diagnostics
+                    .assertOnlyWarnings()
+                    .assertWarningsMatch(
+                        allOf(
+                            diagnosticType(
+                                EmptyMemberRulesToDefaultInitRuleConversionDiagnostic.class),
+                            diagnosticMessage(
+                                equalTo(
+                                    StringUtils.joinLines(
+                                        "The current version of R8 implicitly keeps the default"
+                                            + " constructor for Proguard configuration rules that"
+                                            + " have no member pattern. If the following rule"
+                                            + " should continue to keep the default constructor in"
+                                            + " the next major version of R8, then it must be"
+                                            + " augmented with the member pattern `{ void <init>();"
+                                            + " }` to explicitly keep the default constructor:",
+                                        "-keep class " + Main.class.getTypeName()))))))
+        .inspect(inspector -> assertThat(inspector.clazz(Main.class).init(), isPresent()));
+  }
+
+  @Test
+  public void testFullExplicit() throws Exception {
     testForR8(parameters.getBackend())
         .addInnerClasses(getClass())
         .addKeepClassRules(Main.class)
diff --git a/src/test/testbase/java/com/android/tools/r8/R8TestBuilder.java b/src/test/testbase/java/com/android/tools/r8/R8TestBuilder.java
index 3309783..0b7d432 100644
--- a/src/test/testbase/java/com/android/tools/r8/R8TestBuilder.java
+++ b/src/test/testbase/java/com/android/tools/r8/R8TestBuilder.java
@@ -40,6 +40,7 @@
 import com.android.tools.r8.utils.FileUtils;
 import com.android.tools.r8.utils.InternalOptions;
 import com.android.tools.r8.utils.MapIdTemplateProvider;
+import com.android.tools.r8.utils.OptionalBool;
 import com.android.tools.r8.utils.Pair;
 import com.android.tools.r8.utils.SemanticVersion;
 import com.android.tools.r8.utils.SourceFileTemplateProvider;
@@ -76,7 +77,7 @@
 
   private AllowedDiagnosticMessages allowedDiagnosticMessages = AllowedDiagnosticMessages.NONE;
   private boolean allowUnusedProguardConfigurationRules = false;
-  private boolean enableEmptyMemberRulesToDefaultInitRuleConversion = false;
+  private OptionalBool enableEmptyMemberRulesToDefaultInitRuleConversion = OptionalBool.FALSE;
   private boolean enableIsolatedSplits = false;
   private boolean enableMissingLibraryApiModeling = true;
   private boolean enableStartupLayoutOptimization = true;
@@ -140,8 +141,10 @@
     ToolHelper.addSyntheticProguardRulesConsumerForTesting(
         builder, rules -> box.syntheticProguardRules = rules);
     libraryDesugaringTestConfiguration.configure(builder);
-    builder.setEnableEmptyMemberRulesToDefaultInitRuleConversion(
-        enableEmptyMemberRulesToDefaultInitRuleConversion);
+    if (!enableEmptyMemberRulesToDefaultInitRuleConversion.isUnknown()) {
+      builder.setEnableEmptyMemberRulesToDefaultInitRuleConversion(
+          enableEmptyMemberRulesToDefaultInitRuleConversion.toBoolean());
+    }
     builder.setEnableIsolatedSplits(enableIsolatedSplits);
     builder.setEnableExperimentalMissingLibraryApiModeling(enableMissingLibraryApiModeling);
     builder.setEnableStartupLayoutOptimization(enableStartupLayoutOptimization);
@@ -888,7 +891,12 @@
   public T enableEmptyMemberRulesToDefaultInitRuleConversion(
       boolean enableEmptyMemberRulesToDefaultInitRuleConversion) {
     this.enableEmptyMemberRulesToDefaultInitRuleConversion =
-        enableEmptyMemberRulesToDefaultInitRuleConversion;
+        OptionalBool.of(enableEmptyMemberRulesToDefaultInitRuleConversion);
+    return self();
+  }
+
+  public T clearEnableEmptyMemberRulesToDefaultInitRuleConversion() {
+    this.enableEmptyMemberRulesToDefaultInitRuleConversion = OptionalBool.UNKNOWN;
     return self();
   }
 
diff --git a/tools/create_r8lib.py b/tools/create_r8lib.py
index c8eb00e..1f02869 100755
--- a/tools/create_r8lib.py
+++ b/tools/create_r8lib.py
@@ -95,6 +95,8 @@
             '-agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=*:5005'
         ])
     cmd.append('-Dcom.android.tools.r8.enableKeepAnnotations=1')
+    # TODO(b/356344563): Remove when this is default.
+    cmd.append('-Dcom.android.tools.r8.enableEmptyMemberRulesToDefaultInitRuleConversion=0')
     cmd.extend(['-cp', args.r8compiler, 'com.android.tools.r8.R8'])
     cmd.append(args.r8jar)
     if args.debug_variant: