diff --git a/google-cloud-storage/src/main/java/com/google/cloud/storage/Bucket.java b/google-cloud-storage/src/main/java/com/google/cloud/storage/Bucket.java
index 4160327a8..84222eab2 100644
--- a/google-cloud-storage/src/main/java/com/google/cloud/storage/Bucket.java
+++ b/google-cloud-storage/src/main/java/com/google/cloud/storage/Bucket.java
@@ -1285,7 +1285,7 @@ public boolean deleteDefaultAcl(Entity entity) {
    *
    * @throws StorageException upon failure
    */
-  @TransportCompatibility({Transport.HTTP})
+  @TransportCompatibility({Transport.HTTP, Transport.GRPC})
   public Acl createDefaultAcl(Acl acl) {
     return storage.createDefaultAcl(getName(), acl);
   }
@@ -1304,7 +1304,7 @@ public Acl createDefaultAcl(Acl acl) {
    *
    * @throws StorageException upon failure
    */
-  @TransportCompatibility({Transport.HTTP})
+  @TransportCompatibility({Transport.HTTP, Transport.GRPC})
   public Acl updateDefaultAcl(Acl acl) {
     return storage.updateDefaultAcl(getName(), acl);
   }
diff --git a/google-cloud-storage/src/main/java/com/google/cloud/storage/GrpcStorageImpl.java b/google-cloud-storage/src/main/java/com/google/cloud/storage/GrpcStorageImpl.java
index 73e56bbe2..1ced5cc8c 100644
--- a/google-cloud-storage/src/main/java/com/google/cloud/storage/GrpcStorageImpl.java
+++ b/google-cloud-storage/src/main/java/com/google/cloud/storage/GrpcStorageImpl.java
@@ -68,6 +68,7 @@
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Streams;
 import com.google.common.io.BaseEncoding;
 import com.google.common.io.ByteStreams;
 import com.google.iam.v1.GetIamPolicyRequest;
@@ -936,12 +937,59 @@ public boolean deleteDefaultAcl(String bucket, Entity entity) {
 
   @Override
   public Acl createDefaultAcl(String bucket, Acl acl) {
-    return throwNotYetImplemented(fmtMethodName("createDefaultAcl", String.class, Acl.class));
+    return updateDefaultAcl(bucket, acl);
   }
 
   @Override
   public Acl updateDefaultAcl(String bucket, Acl acl) {
-    return throwNotYetImplemented(fmtMethodName("updateDefaultAcl", String.class, Acl.class));
+    try {
+      com.google.storage.v2.Bucket resp = getBucketDefaultAcls(bucket);
+      ObjectAccessControl encode = codecs.objectAcl().encode(acl);
+      String entity = encode.getEntity();
+
+      Predicate<ObjectAccessControl> entityPredicate = objectAclEntityOrAltEq(entity);
+
+      ImmutableList<ObjectAccessControl> collect =
+          Streams.concat(
+                  resp.getDefaultObjectAclList().stream().filter(entityPredicate.negate()),
+                  Stream.of(encode))
+              .collect(ImmutableList.toImmutableList());
+
+      com.google.storage.v2.Bucket update =
+          com.google.storage.v2.Bucket.newBuilder()
+              .setName(bucketNameCodec.encode(bucket))
+              .addAllDefaultObjectAcl(collect)
+              .build();
+      Opts<BucketTargetOpt> opts =
+          Opts.from(
+              UnifiedOpts.fields(ImmutableSet.of(BucketField.DEFAULT_OBJECT_ACL)),
+              UnifiedOpts.metagenerationMatch(resp.getMetageneration()));
+      UpdateBucketRequest req =
+          opts.updateBucketsRequest()
+              .apply(UpdateBucketRequest.newBuilder())
+              .setBucket(update)
+              .build();
+
+      GrpcCallContext grpcCallContext = GrpcCallContext.createDefault();
+      com.google.storage.v2.Bucket updateResult =
+          Retrying.run(
+              getOptions(),
+              retryAlgorithmManager.getFor(req),
+              () -> storageClient.updateBucketCallable().call(req, grpcCallContext),
+              Decoder.identity());
+
+      //noinspection DataFlowIssue
+      Optional<Acl> first =
+          updateResult.getDefaultObjectAclList().stream()
+              .filter(entityPredicate)
+              .findFirst()
+              .map(codecs.objectAcl()::decode);
+
+      return first.orElseThrow(
+          () -> new StorageException(0, "Acl update call success, but not in response"));
+    } catch (NotFoundException e) {
+      throw StorageException.coalesce(e);
+    }
   }
 
   @Override
diff --git a/google-cloud-storage/src/main/java/com/google/cloud/storage/Storage.java b/google-cloud-storage/src/main/java/com/google/cloud/storage/Storage.java
index ad92aae59..181998983 100644
--- a/google-cloud-storage/src/main/java/com/google/cloud/storage/Storage.java
+++ b/google-cloud-storage/src/main/java/com/google/cloud/storage/Storage.java
@@ -3530,7 +3530,7 @@ PostPolicyV4 generateSignedPostPolicyV4(
    *
    * @throws StorageException upon failure
    */
-  @TransportCompatibility({Transport.HTTP})
+  @TransportCompatibility({Transport.HTTP, Transport.GRPC})
   Acl createDefaultAcl(String bucket, Acl acl);
 
   /**
@@ -3549,7 +3549,7 @@ PostPolicyV4 generateSignedPostPolicyV4(
    *
    * @throws StorageException upon failure
    */
-  @TransportCompatibility({Transport.HTTP})
+  @TransportCompatibility({Transport.HTTP, Transport.GRPC})
   Acl updateDefaultAcl(String bucket, Acl acl);
 
   /**
diff --git a/google-cloud-storage/src/main/java/com/google/cloud/storage/UnifiedOpts.java b/google-cloud-storage/src/main/java/com/google/cloud/storage/UnifiedOpts.java
index 934c2c298..dc5d10bf5 100644
--- a/google-cloud-storage/src/main/java/com/google/cloud/storage/UnifiedOpts.java
+++ b/google-cloud-storage/src/main/java/com/google/cloud/storage/UnifiedOpts.java
@@ -713,7 +713,7 @@ public Mapper<ListObjectsRequest.Builder> listObjects() {
   }
 
   static final class Fields extends RpcOptVal<ImmutableSet<NamedField>>
-      implements ObjectSourceOpt, ObjectListOpt, BucketSourceOpt, BucketListOpt {
+      implements ObjectSourceOpt, ObjectListOpt, BucketSourceOpt, BucketTargetOpt, BucketListOpt {
 
     /**
      * Apiary and gRPC have differing handling of where the field selector is evaluated relative to
@@ -752,6 +752,11 @@ public Mapper<ListBucketsRequest.Builder> listBuckets() {
       return b -> b.setReadMask(FieldMask.newBuilder().addAllPaths(getPaths()).build());
     }
 
+    @Override
+    public Mapper<UpdateBucketRequest.Builder> updateBucket() {
+      return b -> b.setUpdateMask(FieldMask.newBuilder().addAllPaths(getPaths()).build());
+    }
+
     @Override
     public Mapper<GetObjectRequest.Builder> getObject() {
       return b -> b.setReadMask(FieldMask.newBuilder().addAllPaths(getPaths()).build());
diff --git a/google-cloud-storage/src/test/java/com/google/cloud/storage/it/ITAccessTest.java b/google-cloud-storage/src/test/java/com/google/cloud/storage/it/ITAccessTest.java
index 7351227dd..f15a79982 100644
--- a/google-cloud-storage/src/test/java/com/google/cloud/storage/it/ITAccessTest.java
+++ b/google-cloud-storage/src/test/java/com/google/cloud/storage/it/ITAccessTest.java
@@ -33,6 +33,8 @@
 import com.google.cloud.RetryHelper.RetryHelperException;
 import com.google.cloud.http.BaseHttpServiceException;
 import com.google.cloud.storage.Acl;
+import com.google.cloud.storage.Acl.Entity;
+import com.google.cloud.storage.Acl.Project.ProjectRole;
 import com.google.cloud.storage.Acl.Role;
 import com.google.cloud.storage.Acl.User;
 import com.google.cloud.storage.Blob;
@@ -70,6 +72,7 @@
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.Callable;
+import java.util.function.Predicate;
 import java.util.stream.Collector;
 import java.util.stream.Collectors;
 import org.junit.Ignore;
@@ -185,12 +188,108 @@ public void bucket_defaultAcl_list_bucket404() {
     assertThat(storageException.getCode()).isEqualTo(404);
   }
 
+  @Test
+  public void bucket_defaultAcl_create() throws Exception {
+    BucketInfo bucketInfo = BucketInfo.newBuilder(generator.randomBucketName()).build();
+    try (TemporaryBucket tempB =
+        TemporaryBucket.newBuilder().setBucketInfo(bucketInfo).setStorage(storage).build()) {
+      BucketInfo bucket = tempB.getBucket();
+
+      Acl readAll = Acl.of(User.ofAllAuthenticatedUsers(), Role.READER);
+      Acl actual = retry429s(() -> storage.createDefaultAcl(bucket.getName(), readAll), storage);
+
+      assertThat(actual.getEntity()).isEqualTo(readAll.getEntity());
+      assertThat(actual.getRole()).isEqualTo(readAll.getRole());
+      assertThat(actual.getEtag()).isNotEmpty();
+
+      Bucket bucketUpdated =
+          storage.get(bucket.getName(), BucketGetOption.fields(BucketField.values()));
+      assertThat(bucketUpdated.getMetageneration()).isNotEqualTo(bucket.getMetageneration());
+
+      // etags change when updates happen, drop before our comparison
+      List<Acl> expectedAcls = dropEtags(bucket.getDefaultAcl());
+      List<Acl> actualAcls = dropEtags(bucketUpdated.getDefaultAcl());
+      assertThat(actualAcls).containsAtLeastElementsIn(expectedAcls);
+      assertThat(actualAcls).contains(readAll);
+    }
+  }
+
+  @Test
+  public void bucket_defaultAcl_create_bucket404() {
+    Acl readAll = Acl.of(User.ofAllAuthenticatedUsers(), Role.READER);
+    StorageException storageException =
+        assertThrows(
+            StorageException.class,
+            () ->
+                retry429s(
+                    () -> storage.createDefaultAcl(bucket.getName() + "x", readAll), storage));
+
+    assertThat(storageException.getCode()).isEqualTo(404);
+  }
+
+  @Test
+  public void bucket_defaultAcl_update() throws Exception {
+    BucketInfo bucketInfo = BucketInfo.newBuilder(generator.randomBucketName()).build();
+    try (TemporaryBucket tempB =
+        TemporaryBucket.newBuilder().setBucketInfo(bucketInfo).setStorage(storage).build()) {
+      BucketInfo bucket = tempB.getBucket();
+
+      List<Acl> defaultAcls = bucket.getDefaultAcl();
+      assertThat(defaultAcls).isNotEmpty();
+
+      Predicate<Acl> isProjectEditor = hasProjectRole(ProjectRole.EDITORS);
+
+      //noinspection OptionalGetWithoutIsPresent
+      Acl projectEditorAsOwner =
+          defaultAcls.stream().filter(hasRole(Role.OWNER).and(isProjectEditor)).findFirst().get();
+
+      // lower the privileges of project editors to writer from owner
+      Entity entity = projectEditorAsOwner.getEntity();
+      Acl projectEditorAsReader = Acl.of(entity, Role.READER);
+
+      Acl actual =
+          retry429s(
+              () -> storage.updateDefaultAcl(bucket.getName(), projectEditorAsReader), storage);
+
+      assertThat(actual.getEntity()).isEqualTo(projectEditorAsReader.getEntity());
+      assertThat(actual.getRole()).isEqualTo(projectEditorAsReader.getRole());
+      assertThat(actual.getEtag()).isNotEmpty();
+
+      Bucket bucketUpdated =
+          storage.get(bucket.getName(), BucketGetOption.fields(BucketField.values()));
+      assertThat(bucketUpdated.getMetageneration()).isNotEqualTo(bucket.getMetageneration());
+
+      // etags change when updates happen, drop before our comparison
+      List<Acl> expectedAcls =
+          dropEtags(
+              bucket.getDefaultAcl().stream()
+                  .filter(isProjectEditor.negate())
+                  .collect(Collectors.toList()));
+      List<Acl> actualAcls = dropEtags(bucketUpdated.getDefaultAcl());
+      assertThat(actualAcls).containsAtLeastElementsIn(expectedAcls);
+      assertThat(actualAcls).doesNotContain(projectEditorAsOwner);
+      assertThat(actualAcls).contains(projectEditorAsReader);
+    }
+  }
+
+  @Test
+  public void bucket_defaultAcl_update_bucket404() {
+    Acl readAll = Acl.of(User.ofAllAuthenticatedUsers(), Role.READER);
+    StorageException storageException =
+        assertThrows(
+            StorageException.class,
+            () ->
+                retry429s(
+                    () -> storage.updateDefaultAcl(bucket.getName() + "x", readAll), storage));
+
+    assertThat(storageException.getCode()).isEqualTo(404);
+  }
+
   @Test
   @CrossRun.Ignore(transports = Transport.GRPC)
   public void testBucketDefaultAcl() {
     // TODO: break this test up into each of the respective scenarios
     //   2. Delete a default ACL for a specific entity
-    //   3. Create a default ACL for specific entity
     //   4. Update default ACL to change role of a specific entity
 
     // according to https://cloud.google.com/storage/docs/access-control/lists#default
@@ -1026,4 +1125,24 @@ public boolean shouldRetry(Throwable previousThrowable, Object previousResponse)
       }
     }
   }
+
+  private static ImmutableList<Acl> dropEtags(List<Acl> defaultAcls) {
+    return defaultAcls.stream()
+        .map(acl -> Acl.of(acl.getEntity(), acl.getRole()))
+        .collect(ImmutableList.toImmutableList());
+  }
+
+  private static Predicate<Acl> hasRole(Acl.Role expected) {
+    return acl -> acl.getRole().equals(expected);
+  }
+
+  private static Predicate<Acl> hasProjectRole(Acl.Project.ProjectRole expected) {
+    return acl -> {
+      Entity entity = acl.getEntity();
+      if (entity.getType().equals(Entity.Type.PROJECT)) {
+        return ((Acl.Project) entity).getProjectRole().equals(expected);
+      }
+      return false;
+    };
+  }
 }