diff --git a/.github/scripts/hermetic_library_generation.sh b/.github/scripts/hermetic_library_generation.sh
index 1448ab7917..861f28d9bd 100755
--- a/.github/scripts/hermetic_library_generation.sh
+++ b/.github/scripts/hermetic_library_generation.sh
@@ -64,17 +64,14 @@ fi
 
 image_tag=local
 workspace_name="/workspace"
-docker_file="library_generation.Dockerfile"
+baseline_generation_config="baseline_generation_config.yaml"
 message="chore: generate libraries at $(date)"
 
+git checkout "${target_branch}"
 git checkout "${current_branch}"
-# if the last commit doesn't contain changes to generation configuration
-# or Dockerfile, do not generate again as the result will be the same.
-change_of_last_commit="$(git diff-tree --no-commit-id --name-only HEAD~1..HEAD -r)"
-if [[ ! ("${change_of_last_commit}" == *"${generation_config}"* || "${change_of_last_commit}" == *"${docker_file}"*) ]]; then
-    echo "The last commit doesn't contain any changes to the generation_config.yaml or Dockerfile, skipping the whole generation process." || true
-    exit 0
-fi
+
+# copy generation configuration from target branch to current branch.
+git show "${target_branch}":"${generation_config}" > "${baseline_generation_config}"
 
 generator_version=$(mvn help:evaluate -Dexpression=project.version -q -DforceStdout -pl gapic-generator-java)
 echo "Local generator version: ${generator_version}"
@@ -94,10 +91,12 @@ docker run \
   -v "$(pwd):${workspace_name}" \
   -v "$HOME"/.m2:/home/.m2 \
   -e GENERATOR_VERSION="${generator_version}" \
-  gcr.io/cloud-devrel-public-resources/java-library-generation:"${image_tag}"
+  gcr.io/cloud-devrel-public-resources/java-library-generation:"${image_tag}" \
+  --baseline-generation-config-path="${workspace_name}/${baseline_generation_config}" \
+  --current-generation-config-path="${workspace_name}/${generation_config}"
 
 # commit the change to the pull request.
-rm -rdf output googleapis
+rm -rdf output googleapis "${baseline_generation_config}"
 git add --all -- ':!pr_description.txt'
 changed_files=$(git diff --cached --name-only)
 if [[ "${changed_files}" == "" ]]; then
diff --git a/.github/workflows/hermetic_library_generation.yaml b/.github/workflows/hermetic_library_generation.yaml
index ebc9ab770c..9a2cf40d03 100644
--- a/.github/workflows/hermetic_library_generation.yaml
+++ b/.github/workflows/hermetic_library_generation.yaml
@@ -17,10 +17,11 @@ name: Hermetic library generation upon generation config change through pull req
 on:
   pull_request:
 
+env:
+  REPO_FULL_NAME: ${{ github.event.pull_request.head.repo.full_name }}
+  GITHUB_REPOSITORY: ${{ github.repository }}
 jobs:
   library_generation:
-    # skip pull requests come from a forked repository
-    if: github.event.pull_request.head.repo.full_name == github.repository
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v4
@@ -31,6 +32,10 @@ jobs:
       shell: bash
       run: |
         set -x
+        if [[ "${GITHUB_REPOSITORY}" != "${REPO_FULL_NAME}" ]]; then
+          echo "This PR comes from a fork. Skip library generation."
+          exit 0
+        fi
         [ -z "$(git config user.email)" ] && git config --global user.email "cloud-java-bot@google.com"
         [ -z "$(git config user.name)" ] && git config --global user.name "cloud-java-bot"
         bash .github/scripts/hermetic_library_generation.sh \
diff --git a/library_generation/cli/entry_point.py b/library_generation/cli/entry_point.py
index 7eefeeca05..d69dde1b77 100644
--- a/library_generation/cli/entry_point.py
+++ b/library_generation/cli/entry_point.py
@@ -17,6 +17,7 @@
 import click as click
 from library_generation.generate_pr_description import generate_pr_descriptions
 from library_generation.generate_repo import generate_from_yaml
+from library_generation.model.config_change import ConfigChange
 from library_generation.model.generation_config import from_yaml
 from library_generation.utils.generation_config_comparator import compare_config
 
@@ -145,11 +146,10 @@ def __generate_repo_and_pr_description_impl(
         baseline_config=from_yaml(baseline_generation_config_path),
         current_config=from_yaml(current_generation_config_path),
     )
-    # pass None if this is not a monorepo in order to trigger the full
-    # generation
+    # pass None if we want to fully generate the repository.
     target_library_names = (
         config_change.get_changed_libraries()
-        if config_change.current_config.is_monorepo()
+        if not _needs_full_repo_generation(config_change=config_change)
         else None
     )
     generate_from_yaml(
@@ -163,6 +163,15 @@ def __generate_repo_and_pr_description_impl(
     )
 
 
+def _needs_full_repo_generation(config_change: ConfigChange) -> bool:
+    """
+    Whether you should need a full repo generation, i.e., generate all
+    libraries in the generation configuration.
+    """
+    current_config = config_change.current_config
+    return not current_config.is_monorepo() or current_config.contains_common_protos()
+
+
 @main.command()
 @click.option(
     "--generation-config-path",
diff --git a/library_generation/test/cli/entry_point_unit_tests.py b/library_generation/test/cli/entry_point_unit_tests.py
index 66756be500..e05c64de55 100644
--- a/library_generation/test/cli/entry_point_unit_tests.py
+++ b/library_generation/test/cli/entry_point_unit_tests.py
@@ -138,3 +138,56 @@ def test_generate_non_monorepo_with_changes_triggers_full_generation(
         generate_from_yaml.assert_called_with(
             config=ANY, repository_path=ANY, target_library_names=None
         )
+
+    @patch("library_generation.cli.entry_point.generate_from_yaml")
+    @patch("library_generation.cli.entry_point.generate_pr_descriptions")
+    def test_generate_monorepo_with_common_protos_triggers_full_generation(
+        self,
+        generate_pr_descriptions,
+        generate_from_yaml,
+    ):
+        """
+        this tests confirms the behavior of generation of a monorepo with
+        common protos.
+        generate() should call generate_from_yaml() with
+        target_library_names=None in order to trigger the full generation
+        """
+        config_path = f"{test_resource_dir}/monorepo_with_common_protos.yaml"
+        self.assertTrue(from_yaml(config_path).is_monorepo())
+        # we call the implementation method directly since click
+        # does special handling when a method is annotated with @main.command()
+        generate_impl(
+            baseline_generation_config_path=config_path,
+            current_generation_config_path=config_path,
+            repository_path=".",
+        )
+        generate_from_yaml.assert_called_with(
+            config=ANY, repository_path=ANY, target_library_names=None
+        )
+
+    @patch("library_generation.cli.entry_point.generate_from_yaml")
+    @patch("library_generation.cli.entry_point.generate_pr_descriptions")
+    def test_generate_monorepo_without_common_protos_does_not_trigger_full_generation(
+        self,
+        generate_pr_descriptions,
+        generate_from_yaml,
+    ):
+        """
+        this tests confirms the behavior of generation of a monorepo without
+        common protos.
+        generate() should call generate_from_yaml() with
+        target_library_names=changed libraries which does not trigger the full
+        generation.
+        """
+        config_path = f"{test_resource_dir}/monorepo_without_common_protos.yaml"
+        self.assertTrue(from_yaml(config_path).is_monorepo())
+        # we call the implementation method directly since click
+        # does special handling when a method is annotated with @main.command()
+        generate_impl(
+            baseline_generation_config_path=config_path,
+            current_generation_config_path=config_path,
+            repository_path=".",
+        )
+        generate_from_yaml.assert_called_with(
+            config=ANY, repository_path=ANY, target_library_names=[]
+        )
diff --git a/library_generation/test/generate_library_unit_tests.py b/library_generation/test/generate_library_unit_tests.py
index 86a6a5d637..7bc14e3e20 100644
--- a/library_generation/test/generate_library_unit_tests.py
+++ b/library_generation/test/generate_library_unit_tests.py
@@ -1,3 +1,16 @@
+# Copyright 2024 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
+#
+#     https://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.
 import subprocess
 import unittest
 import os
@@ -66,13 +79,13 @@ def _run_command_and_get_sdout(self, command, **kwargs):
     def test_get_grpc_version_with_no_env_var_fails(self):
         # the absence of DOCKER_GRPC_VERSION will make this function to fail
         result = self._run_command("get_grpc_version")
-        self.assertEquals(1, result.returncode)
+        self.assertEqual(1, result.returncode)
         self.assertRegex(result.stdout.decode(), "DOCKER_GRPC_VERSION is not set")
 
     def test_get_protoc_version_with_no_env_var_fails(self):
         # the absence of DOCKER_PROTOC_VERSION will make this function to fail
         result = self._run_command("get_protoc_version")
-        self.assertEquals(1, result.returncode)
+        self.assertEqual(1, result.returncode)
         self.assertRegex(result.stdout.decode(), "DOCKER_PROTOC_VERSION is not set")
 
     def test_download_tools_without_baked_generator_fails(self):
@@ -92,5 +105,5 @@ def test_download_tools_without_baked_generator_fails(self):
         result = self._run_command(
             f"download_tools {test_protoc_version} {test_grpc_version} {self.TEST_ARCHITECTURE}"
         )
-        self.assertEquals(1, result.returncode)
+        self.assertEqual(1, result.returncode)
         self.assertRegex(result.stdout.decode(), "Please configure your environment")
diff --git a/library_generation/test/resources/test-config/monorepo_with_common_protos.yaml b/library_generation/test/resources/test-config/monorepo_with_common_protos.yaml
new file mode 100644
index 0000000000..6d4c94444a
--- /dev/null
+++ b/library_generation/test/resources/test-config/monorepo_with_common_protos.yaml
@@ -0,0 +1,43 @@
+googleapis_commitish: 6a474b31c53cc1797710206824a17b364a835d2d
+gapic_generator_version: 2.34.0
+# the libraries are ordered with respect to library name, which is
+# java-{library.library_name} or java-{library.api-shortname} when
+# library.library_name is not defined.
+libraries:
+- api_shortname: common-protos
+  name_pretty: Common Protos
+  product_documentation: https://github.com/googleapis/api-common-protos
+  api_description: Protobuf classes for Google's common protos.
+  release_level: stable
+  client_documentation: https://cloud.google.com/java/docs/reference/proto-google-common-protos/latest/history
+  distribution_name: com.google.api.grpc:proto-google-common-protos
+  excluded_dependencies: "proto-google-common-protos,grpc-google-common-protos,proto-google-common-protos-parent"
+  excluded_poms: "proto-google-common-protos-bom,proto-google-common-protos"
+  library_type: OTHER
+  GAPICs:
+  - proto_path: google/api
+  - proto_path: google/apps/card/v1
+  - proto_path: google/cloud
+  - proto_path: google/cloud/audit
+  - proto_path: google/cloud/location
+  - proto_path: google/geo/type
+  - proto_path: google/logging/type
+  - proto_path: google/longrunning
+  - proto_path: google/rpc
+  - proto_path: google/rpc/context
+  - proto_path: google/shopping/type
+  - proto_path: google/type
+- api_shortname: iam
+  name_pretty: IAM
+  product_documentation: https://cloud.google.com/iam
+  api_description: Manages access control for Google Cloud Platform resources
+  release_level: stable
+  client_documentation: https://cloud.google.com/java/docs/reference/proto-google-iam-v1/latest/overview
+  distribution_name: com.google.api.grpc:proto-google-iam-v1
+  excluded_dependencies: "grpc-google-iam-v1"
+  excluded_poms: "proto-google-iam-v1-bom,google-iam-policy,proto-google-iam-v1"
+  library_type: OTHER
+  GAPICs:
+  - proto_path: google/iam/v1
+  - proto_path: google/iam/v2
+  - proto_path: google/iam/v2beta
\ No newline at end of file
diff --git a/library_generation/test/resources/test-config/monorepo_without_common_protos.yaml b/library_generation/test/resources/test-config/monorepo_without_common_protos.yaml
new file mode 100644
index 0000000000..ca21ccfb01
--- /dev/null
+++ b/library_generation/test/resources/test-config/monorepo_without_common_protos.yaml
@@ -0,0 +1,33 @@
+gapic_generator_version: 2.34.0
+protoc_version: 25.2
+googleapis_commitish: 1a45bf7393b52407188c82e63101db7dc9c72026
+libraries_bom_version: 26.37.0
+libraries:
+  - api_shortname: cloudasset
+    name_pretty: Cloud Asset Inventory
+    product_documentation: "https://cloud.google.com/resource-manager/docs/cloud-asset-inventory/overview"
+    api_description: "provides inventory services based on a time series database."
+    library_name: "asset"
+    client_documentation: "https://cloud.google.com/java/docs/reference/google-cloud-asset/latest/overview"
+    distribution_name: "com.google.cloud:google-cloud-asset"
+    release_level: "stable"
+    issue_tracker: "https://issuetracker.google.com/issues/new?component=187210&template=0"
+    api_reference: "https://cloud.google.com/resource-manager/docs/cloud-asset-inventory/overview"
+    GAPICs:
+      - proto_path: google/cloud/asset/v1
+      - proto_path: google/cloud/asset/v1p1beta1
+      - proto_path: google/cloud/asset/v1p2beta1
+      - proto_path: google/cloud/asset/v1p5beta1
+      - proto_path: google/cloud/asset/v1p7beta1
+  - api_shortname: cloudbuild
+    name_pretty: Cloud Build
+    product_documentation: https://cloud.google.com/cloud-build/
+    api_description: lets you build software quickly across all languages. Get complete
+        control over defining custom workflows for building, testing, and deploying across
+        multiple environments such as VMs, serverless, Kubernetes, or Firebase.
+    release_level: stable
+    distribution_name: com.google.cloud:google-cloud-build
+    issue_tracker: https://issuetracker.google.com/savedsearches/5226584
+    GAPICs:
+       - proto_path: google/devtools/cloudbuild/v1
+       - proto_path: google/devtools/cloudbuild/v2