diff --git a/proto/pom.xml b/proto/pom.xml
index 33d7a4ebee..253992b7b1 100644
--- a/proto/pom.xml
+++ b/proto/pom.xml
@@ -32,7 +32,7 @@
     <!-- This is duplicated here because that is recommended by `artifact:check-buildplan` -->
     <project.build.outputTimestamp>2023-01-01T00:00:00Z</project.build.outputTimestamp>
 
-    <protobufVersion>3.25.3</protobufVersion>
+    <protobufVersion>4.26.1</protobufVersion>
   </properties>
 
   <licenses>
diff --git a/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithAnnotationsTest.java b/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithAnnotationsTest.java
index c56ade3ad3..9be26bfe16 100644
--- a/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithAnnotationsTest.java
+++ b/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithAnnotationsTest.java
@@ -28,7 +28,7 @@
 import com.google.gson.protobuf.generated.Bag.OuterMessage;
 import com.google.gson.protobuf.generated.Bag.ProtoWithAnnotations;
 import com.google.gson.protobuf.generated.Bag.ProtoWithAnnotations.InnerMessage;
-import com.google.protobuf.GeneratedMessageV3;
+import com.google.protobuf.GeneratedMessage;
 import org.junit.Before;
 import org.junit.Test;
 
@@ -51,18 +51,18 @@ public void setUp() throws Exception {
             .addSerializedEnumValueExtension(Annotations.serializedValue);
     gson =
         new GsonBuilder()
-            .registerTypeHierarchyAdapter(GeneratedMessageV3.class, protoTypeAdapter.build())
+            .registerTypeHierarchyAdapter(GeneratedMessage.class, protoTypeAdapter.build())
             .create();
     gsonWithEnumNumbers =
         new GsonBuilder()
             .registerTypeHierarchyAdapter(
-                GeneratedMessageV3.class,
+                GeneratedMessage.class,
                 protoTypeAdapter.setEnumSerialization(EnumSerialization.NUMBER).build())
             .create();
     gsonWithLowerHyphen =
         new GsonBuilder()
             .registerTypeHierarchyAdapter(
-                GeneratedMessageV3.class,
+                GeneratedMessage.class,
                 protoTypeAdapter
                     .setFieldNameSerializationFormat(
                         CaseFormat.LOWER_UNDERSCORE, CaseFormat.LOWER_HYPHEN)
diff --git a/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithComplexAndRepeatedFieldsTest.java b/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithComplexAndRepeatedFieldsTest.java
index 1c3bc1c891..367aefc43b 100644
--- a/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithComplexAndRepeatedFieldsTest.java
+++ b/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithComplexAndRepeatedFieldsTest.java
@@ -27,7 +27,7 @@
 import com.google.gson.protobuf.generated.Bag.ProtoWithDifferentCaseFormat;
 import com.google.gson.protobuf.generated.Bag.ProtoWithRepeatedFields;
 import com.google.gson.protobuf.generated.Bag.SimpleProto;
-import com.google.protobuf.GeneratedMessageV3;
+import com.google.protobuf.GeneratedMessage;
 import org.junit.Before;
 import org.junit.Test;
 
@@ -45,7 +45,7 @@ public void setUp() throws Exception {
     gson =
         new GsonBuilder()
             .registerTypeHierarchyAdapter(
-                GeneratedMessageV3.class,
+                GeneratedMessage.class,
                 ProtoTypeAdapter.newBuilder()
                     .setEnumSerialization(EnumSerialization.NUMBER)
                     .build())
@@ -53,7 +53,7 @@ public void setUp() throws Exception {
     upperCamelGson =
         new GsonBuilder()
             .registerTypeHierarchyAdapter(
-                GeneratedMessageV3.class,
+                GeneratedMessage.class,
                 ProtoTypeAdapter.newBuilder()
                     .setFieldNameSerializationFormat(
                         CaseFormat.LOWER_UNDERSCORE, CaseFormat.UPPER_CAMEL)
diff --git a/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithPrimitiveTypesTest.java b/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithPrimitiveTypesTest.java
index 57ab2df7ef..4bfd7241c4 100644
--- a/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithPrimitiveTypesTest.java
+++ b/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithPrimitiveTypesTest.java
@@ -24,7 +24,7 @@
 import com.google.gson.protobuf.ProtoTypeAdapter;
 import com.google.gson.protobuf.ProtoTypeAdapter.EnumSerialization;
 import com.google.gson.protobuf.generated.Bag.SimpleProto;
-import com.google.protobuf.GeneratedMessageV3;
+import com.google.protobuf.GeneratedMessage;
 import org.junit.Before;
 import org.junit.Test;
 
@@ -36,7 +36,7 @@ public void setUp() throws Exception {
     gson =
         new GsonBuilder()
             .registerTypeHierarchyAdapter(
-                GeneratedMessageV3.class,
+                GeneratedMessage.class,
                 ProtoTypeAdapter.newBuilder()
                     .setEnumSerialization(EnumSerialization.NUMBER)
                     .build())