diff --git a/spanner/Gemfile b/spanner/Gemfile
index 51217dfd5..431c3c4df 100644
--- a/spanner/Gemfile
+++ b/spanner/Gemfile
@@ -15,6 +15,7 @@
 source "https://rubygems.org"
 
 gem "google-cloud-spanner"
+gem "mutex_m"
 
 group :test do
   gem "google-apis-iam_v1"
diff --git a/spanner/Gemfile.lock b/spanner/Gemfile.lock
index bf34bf7d2..f09e7f98e 100644
--- a/spanner/Gemfile.lock
+++ b/spanner/Gemfile.lock
@@ -1,26 +1,31 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    addressable (2.8.6)
-      public_suffix (>= 2.0.2, < 6.0)
-    base64 (0.2.0)
-    concurrent-ruby (1.2.3)
+    addressable (2.8.9)
+      public_suffix (>= 2.0.2, < 8.0)
+    base64 (0.3.0)
+    bigdecimal (3.3.1)
+    concurrent-ruby (1.3.6)
     declarative (0.0.20)
     diff-lcs (1.5.1)
-    faraday (2.9.0)
-      faraday-net_http (>= 2.0, < 3.2)
-    faraday-net_http (3.1.0)
-      net-http
-    faraday-retry (2.2.0)
+    faraday (2.14.1)
+      faraday-net_http (>= 2.0, < 3.5)
+      json
+      logger
+    faraday-net_http (3.4.2)
+      net-http (~> 0.5)
+    faraday-retry (2.4.0)
       faraday (~> 2.0)
-    gapic-common (0.21.1)
+    gapic-common (1.3.0)
       faraday (>= 1.9, < 3.a)
       faraday-retry (>= 1.0, < 3.a)
-      google-protobuf (~> 3.18)
-      googleapis-common-protos (>= 1.4.0, < 2.a)
-      googleapis-common-protos-types (>= 1.11.0, < 2.a)
-      googleauth (~> 1.9)
-      grpc (~> 1.59)
+      google-cloud-env (~> 2.2)
+      google-logging-utils (~> 0.1)
+      google-protobuf (~> 4.26)
+      googleapis-common-protos (~> 1.6)
+      googleapis-common-protos-types (~> 1.15)
+      googleauth (~> 1.12)
+      grpc (~> 1.66)
     google-apis-core (0.14.0)
       addressable (~> 2.5, >= 2.5.1)
       googleauth (~> 1.9)
@@ -31,59 +36,69 @@ GEM
       rexml
     google-apis-iam_v1 (0.54.0)
       google-apis-core (>= 0.14.0, < 2.a)
-    google-cloud-core (1.6.1)
+    google-cloud-core (1.8.0)
       google-cloud-env (>= 1.0, < 3.a)
       google-cloud-errors (~> 1.0)
-    google-cloud-env (2.1.1)
+    google-cloud-env (2.3.1)
+      base64 (~> 0.2)
       faraday (>= 1.0, < 3.a)
-    google-cloud-errors (1.3.1)
-    google-cloud-spanner (2.21.0)
+    google-cloud-errors (1.5.0)
+    google-cloud-spanner (2.35.0)
+      bigdecimal (~> 3.0)
       concurrent-ruby (~> 1.0)
-      google-cloud-core (~> 1.5)
-      google-cloud-spanner-admin-database-v1 (~> 0.1)
-      google-cloud-spanner-admin-instance-v1 (~> 0.1)
-      google-cloud-spanner-v1 (~> 0.2)
-    google-cloud-spanner-admin-database-v1 (0.17.1)
-      gapic-common (>= 0.21.1, < 2.a)
+      google-cloud-core (~> 1.7)
+      google-cloud-spanner-admin-database-v1 (~> 1.4)
+      google-cloud-spanner-admin-instance-v1 (~> 1.6)
+      google-cloud-spanner-v1 (~> 1.6)
+    google-cloud-spanner-admin-database-v1 (1.11.1)
+      gapic-common (~> 1.2)
       google-cloud-errors (~> 1.0)
-      grpc-google-iam-v1 (~> 1.1)
-    google-cloud-spanner-admin-instance-v1 (0.13.2)
-      gapic-common (>= 0.21.1, < 2.a)
+      grpc-google-iam-v1 (~> 1.11)
+    google-cloud-spanner-admin-instance-v1 (1.6.0)
+      gapic-common (>= 0.25.0, < 2.a)
       google-cloud-errors (~> 1.0)
       grpc-google-iam-v1 (~> 1.1)
-    google-cloud-spanner-v1 (0.24.0)
-      gapic-common (>= 0.21.1, < 2.a)
+    google-cloud-spanner-v1 (1.15.0)
+      gapic-common (~> 1.2)
       google-cloud-errors (~> 1.0)
-    google-protobuf (3.25.3)
-    googleapis-common-protos (1.5.0)
-      google-protobuf (~> 3.18)
+    google-logging-utils (0.2.0)
+    google-protobuf (4.34.0)
+      bigdecimal
+      rake (~> 13.3)
+    googleapis-common-protos (1.7.0)
+      google-protobuf (>= 3.18, < 5.a)
       googleapis-common-protos-types (~> 1.7)
       grpc (~> 1.41)
-    googleapis-common-protos-types (1.13.0)
-      google-protobuf (~> 3.18)
-    googleauth (1.11.0)
+    googleapis-common-protos-types (1.22.0)
+      google-protobuf (~> 4.26)
+    googleauth (1.16.2)
       faraday (>= 1.0, < 3.a)
-      google-cloud-env (~> 2.1)
-      jwt (>= 1.4, < 3.0)
+      google-cloud-env (~> 2.2)
+      google-logging-utils (~> 0.1)
+      jwt (>= 1.4, < 4.0)
       multi_json (~> 1.11)
       os (>= 0.9, < 2.0)
       signet (>= 0.16, < 2.a)
-    grpc (1.62.0)
-      google-protobuf (~> 3.25)
+    grpc (1.78.1)
+      google-protobuf (>= 3.25, < 5.0)
       googleapis-common-protos-types (~> 1.0)
-    grpc-google-iam-v1 (1.7.0)
-      google-protobuf (~> 3.18)
-      googleapis-common-protos (~> 1.4)
+    grpc-google-iam-v1 (1.11.0)
+      google-protobuf (>= 3.18, < 5.a)
+      googleapis-common-protos (~> 1.7.0)
       grpc (~> 1.41)
     httpclient (2.8.3)
-    jwt (2.8.0)
+    json (2.19.1)
+    jwt (3.1.2)
       base64
+    logger (1.7.0)
     mini_mime (1.1.5)
-    multi_json (1.15.0)
-    net-http (0.4.1)
-      uri
+    multi_json (1.19.1)
+    mutex_m (0.3.0)
+    net-http (0.9.1)
+      uri (>= 0.11.1)
     os (1.1.4)
-    public_suffix (5.0.4)
+    public_suffix (7.0.5)
+    rake (13.3.1)
     representable (3.2.0)
       declarative (< 0.1.0)
       trailblazer-option (>= 0.1.1, < 0.2.0)
@@ -105,14 +120,14 @@ GEM
     rspec-support (3.13.1)
     rspec_junit_formatter (0.6.0)
       rspec-core (>= 2, < 4, != 2.12.0)
-    signet (0.19.0)
+    signet (0.21.0)
       addressable (~> 2.8)
       faraday (>= 0.17.5, < 3.a)
-      jwt (>= 1.5, < 3.0)
+      jwt (>= 1.5, < 4.0)
       multi_json (~> 1.10)
     trailblazer-option (0.1.2)
     uber (0.1.0)
-    uri (0.13.0)
+    uri (1.1.1)
 
 PLATFORMS
   ruby
@@ -120,6 +135,7 @@ PLATFORMS
 DEPENDENCIES
   google-apis-iam_v1
   google-cloud-spanner
+  mutex_m
   retriable
   rspec
   rspec_junit_formatter
diff --git a/spanner/spanner_batch_write.rb b/spanner/spanner_batch_write.rb
new file mode 100644
index 000000000..195776340
--- /dev/null
+++ b/spanner/spanner_batch_write.rb
@@ -0,0 +1,58 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# [START spanner_batch_write_at_least_once]
+require "google/cloud/spanner"
+
+##
+# This is a snippet for showcasing how to apply a batch of mutations groups.
+# All mutations in a group are applied atomically.
+#
+# @param project_id  [String] The ID of the Google Cloud project.
+# @param instance_id [String] The ID of the spanner instance.
+# @param database_id [String] The ID of the database.
+#
+def spanner_batch_write project_id:, instance_id:, database_id:
+  spanner = Google::Cloud::Spanner.new project: project_id
+  client  = spanner.client instance_id, database_id
+
+  results = client.batch_write do |b|
+    # First mutation group
+    b.mutation_group do |mg|
+      mg.upsert "Singers", [{ SingerId: 16, FirstName: "Scarlet", LastName: "Terry" }]
+    end
+
+    # Second mutation group
+    b.mutation_group do |mg|
+      mg.upsert "Singers", [
+        { SingerId: 17, FirstName: "Marc" },
+        { SingerId: 18, FirstName: "Catalina", LastName: "Smith" }
+      ]
+      mg.upsert "Albums", [
+        { SingerId: 17, AlbumId: 1, AlbumTitle: "Total Junk" },
+        { SingerId: 18, AlbumId: 2, AlbumTitle: "Go, Go, Go" }
+      ]
+    end
+  end
+
+  results.each do |response|
+    if response.ok?
+      puts "Mutation group indexes applied: #{response.indexes}"
+    else
+      puts "Mutation group failed to apply: #{response.indexes}"
+      puts "Error: #{response.status.message}"
+    end
+  end
+end
+# [END spanner_batch_write_at_least_once]
diff --git a/spanner/spec/spanner_batch_write_spec.rb b/spanner/spec/spanner_batch_write_spec.rb
new file mode 100644
index 000000000..867229005
--- /dev/null
+++ b/spanner/spec/spanner_batch_write_spec.rb
@@ -0,0 +1,39 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+require "spec_helper"
+require_relative "../spanner_batch_write"
+
+describe "spanner_batch_write" do
+  before :all do
+    create_singers_albums_database
+  end
+
+  after :all do
+    cleanup_database_resources
+  end
+
+  it "applies mutation groups" do
+    expect {
+      spanner_batch_write project_id: @project_id,
+                          instance_id: @instance_id,
+                          database_id: @database_id
+    }.to output(/Mutation group indexes applied: (\[0, 1\]|\[0\].*\[1\])/m).to_stdout
+
+    # Verify that the records were inserted
+    client = @spanner.client @instance_id, @database_id
+    results = client.execute "SELECT COUNT(*) FROM Singers"
+    expect(results.rows.first[0]).to eq 3 # 16, 17, 18
+  end
+end