diff --git a/hermetic_build/library_generation/owlbot/src/fix_poms.py b/hermetic_build/library_generation/owlbot/src/fix_poms.py
index 9ee7514a4d..1a2fc8e1ac 100644
--- a/hermetic_build/library_generation/owlbot/src/fix_poms.py
+++ b/hermetic_build/library_generation/owlbot/src/fix_poms.py
@@ -358,8 +358,11 @@ def main(versions_file, monorepo):
     with open(".repo-metadata.json", "r") as fp:
         repo_metadata = json.load(fp)
     group_id, artifact_id = repo_metadata["distribution_name"].split(":")
+    # Use api_shortname from repo_metadata as the key for versions.txt
+    release_please_key = repo_metadata["api_shortname"]
     name = repo_metadata["name_pretty"]
     existing_modules = load_versions(versions_file, group_id)
+    original_modules = set(existing_modules.keys())
     print(f"monorepo? {monorepo}")
 
     # extra modules that need to be manages in versions.txt
@@ -456,6 +459,7 @@ def main(versions_file, monorepo):
                 parent_module=parent_module,
                 main_module=main_module,
                 monorepo=monorepo,
+                release_please_key=release_please_key,
             )
             if (
                 path not in excluded_dependencies_list
@@ -498,6 +502,7 @@ def main(versions_file, monorepo):
                 main_module=main_module,
                 proto_module=existing_modules[proto_artifact_id],
                 monorepo=monorepo,
+                release_please_key=release_please_key,
             )
             if (
                 path not in excluded_dependencies_list
@@ -549,6 +554,7 @@ def main(versions_file, monorepo):
             proto_modules=proto_modules,
             grpc_modules=grpc_modules,
             monorepo=monorepo,
+            release_please_key=release_please_key,
         )
 
     if os.path.isfile(f"{artifact_id}-bom/pom.xml"):
@@ -567,6 +573,7 @@ def main(versions_file, monorepo):
             main_module=main_module,
             monorepo=monorepo,
             monorepo_version=monorepo_version,
+            release_please_key=release_please_key,
         )
 
     if os.path.isfile("pom.xml"):
@@ -584,24 +591,51 @@ def main(versions_file, monorepo):
             name=name,
             monorepo=monorepo,
             monorepo_version=monorepo_version,
+            release_please_key=release_please_key,
         )
 
     print(f"updating modules in {versions_file}")
-    existing_modules.pop(parent_artifact_id)
 
-    # add extra modules to versions.txt
+    # existing_modules contains all components, needed for pom.xml rendering.
+
+    versions_txt_modules = {}
+    # Start with all modules that were in the original versions.txt
+    for key in original_modules:
+        if key in existing_modules:
+            versions_txt_modules[key] = existing_modules[key]
+
+    # If this is a new library (release_please_key was not in original_modules),
+    # add the single consolidated entry to our versions.txt dictionary.
+    if release_please_key not in original_modules:
+        versions_txt_modules[release_please_key] = module.Module(
+            group_id=group_id,
+            artifact_id=release_please_key,
+            version=main_module.version,
+            release_version=main_module.release_version,
+        )
+
+    # Add extra managed modules if they aren't already included
     for dependency_module in extra_managed_modules:
-        if dependency_module not in existing_modules:
-            existing_modules[dependency_module] = module.Module(
-                group_id=__proto_group_id(group_id),
-                artifact_id=dependency_module,
-                version=main_module.version,
-                release_version=main_module.release_version,
-            )
+        if dependency_module not in versions_txt_modules:
+            # These should already be in existing_modules if loaded from versions.txt
+            if dependency_module in existing_modules:
+                versions_txt_modules[dependency_module] = existing_modules[
+                    dependency_module
+                ]
+            # This else block should ideally not be reached in the monorepo case.
+            else:
+                versions_txt_modules[dependency_module] = module.Module(
+                    group_id=__proto_group_id(group_id),
+                    artifact_id=dependency_module,
+                    version=main_module.version,
+                    release_version=main_module.release_version,
+                )
+
+    # Render versions.txt using the specially prepared versions_txt_modules
     templates.render(
         template_name="versions.txt.j2",
         output_name=versions_file,
-        modules=existing_modules.values(),
+        modules=versions_txt_modules.values(),
     )
 
 
diff --git a/hermetic_build/library_generation/owlbot/templates/poms/bom_pom.xml.j2 b/hermetic_build/library_generation/owlbot/templates/poms/bom_pom.xml.j2
index ddcef5226f..dcd930c1ae 100644
--- a/hermetic_build/library_generation/owlbot/templates/poms/bom_pom.xml.j2
+++ b/hermetic_build/library_generation/owlbot/templates/poms/bom_pom.xml.j2
@@ -3,7 +3,7 @@
   <modelVersion>4.0.0</modelVersion>
   <groupId>{{main_module.group_id}}</groupId>
   <artifactId>{{main_module.artifact_id}}-bom</artifactId>
-  <version>{{main_module.version}}</version><!-- {x-version-update:{{main_module.artifact_id}}:current} -->
+  <version>{{main_module.version}}</version><!-- {x-version-update:{{release_please_key}}:current} -->
   <packaging>pom</packaging>
   {% if monorepo -%}
   <parent>
@@ -34,7 +34,7 @@
       <dependency>
         <groupId>{{module.group_id}}</groupId>
         <artifactId>{{module.artifact_id}}</artifactId>
-        <version>{{module.version}}</version><!-- {x-version-update:{{module.artifact_id}}:current} -->
+        <version>{{module.version}}</version><!-- {x-version-update:{{release_please_key}}:current} -->
       </dependency>{% endfor %}
     </dependencies>
   </dependencyManagement>
diff --git a/hermetic_build/library_generation/owlbot/templates/poms/cloud_pom.xml.j2 b/hermetic_build/library_generation/owlbot/templates/poms/cloud_pom.xml.j2
index d0ae8cd7c5..3087201693 100644
--- a/hermetic_build/library_generation/owlbot/templates/poms/cloud_pom.xml.j2
+++ b/hermetic_build/library_generation/owlbot/templates/poms/cloud_pom.xml.j2
@@ -3,7 +3,7 @@
   <modelVersion>4.0.0</modelVersion>
   <groupId>{{module.group_id}}</groupId>
   <artifactId>{{module.artifact_id}}</artifactId>
-  <version>{{module.version}}</version><!-- {x-version-update:{{module.artifact_id}}:current} -->
+  <version>{{module.version}}</version><!-- {x-version-update:{{release_please_key}}:current} -->
   <packaging>jar</packaging>
   <name>Google {{name}}</name>
   {%- if not monorepo %}
@@ -13,7 +13,7 @@
   <parent>
     <groupId>{{parent_module.group_id}}</groupId>
     <artifactId>{{parent_module.artifact_id}}</artifactId>
-    <version>{{parent_module.version}}</version><!-- {x-version-update:{{module.artifact_id}}:current} -->
+    <version>{{parent_module.version}}</version><!-- {x-version-update:{{release_please_key}}:current} -->
   </parent>
   <properties>
     <site.installationModule>{{module.artifact_id}}</site.installationModule>
diff --git a/hermetic_build/library_generation/owlbot/templates/poms/grpc_pom.xml.j2 b/hermetic_build/library_generation/owlbot/templates/poms/grpc_pom.xml.j2
index 514861e7a7..4390cf92c0 100644
--- a/hermetic_build/library_generation/owlbot/templates/poms/grpc_pom.xml.j2
+++ b/hermetic_build/library_generation/owlbot/templates/poms/grpc_pom.xml.j2
@@ -4,13 +4,13 @@
   <modelVersion>4.0.0</modelVersion>
   <groupId>{{module.group_id}}</groupId>
   <artifactId>{{module.artifact_id}}</artifactId>
-  <version>{{module.version}}</version><!-- {x-version-update:{{module.artifact_id}}:current} -->
+  <version>{{module.version}}</version><!-- {x-version-update:{{release_please_key}}:current} -->
   <name>{{module.artifact_id}}</name>
   <description>GRPC library for {{main_module.artifact_id}}</description>
   <parent>
     <groupId>{{parent_module.group_id}}</groupId>
     <artifactId>{{parent_module.artifact_id}}</artifactId>
-    <version>{{parent_module.version}}</version><!-- {x-version-update:{{main_module.artifact_id}}:current} -->
+    <version>{{parent_module.version}}</version><!-- {x-version-update:{{release_please_key}}:current} -->
   </parent>
   <dependencies>
     <dependency>
diff --git a/hermetic_build/library_generation/owlbot/templates/poms/parent_pom.xml.j2 b/hermetic_build/library_generation/owlbot/templates/poms/parent_pom.xml.j2
index dcf922340e..2b87c0f601 100644
--- a/hermetic_build/library_generation/owlbot/templates/poms/parent_pom.xml.j2
+++ b/hermetic_build/library_generation/owlbot/templates/poms/parent_pom.xml.j2
@@ -4,7 +4,7 @@
   <groupId>{{main_module.group_id}}</groupId>
   <artifactId>{{main_module.artifact_id}}-parent</artifactId>
   <packaging>pom</packaging>
-  <version>{{main_module.version}}</version><!-- {x-version-update:{{main_module.artifact_id}}:current} -->
+  <version>{{main_module.version}}</version><!-- {x-version-update:{{release_please_key}}:current} -->
   <name>Google {{name}} Parent</name>
   <description>
     Java idiomatic client for Google Cloud Platform services.
@@ -37,7 +37,7 @@
 {% for module in modules %}      <dependency>
         <groupId>{{module.group_id}}</groupId>
         <artifactId>{{module.artifact_id}}</artifactId>
-        <version>{{module.version}}</version><!-- {x-version-update:{{module.artifact_id}}:current} -->
+        <version>{{module.version}}</version><!-- {x-version-update:{{release_please_key}}:current} -->
       </dependency>
 {% endfor %}
     </dependencies>
diff --git a/hermetic_build/library_generation/owlbot/templates/poms/proto_pom.xml.j2 b/hermetic_build/library_generation/owlbot/templates/poms/proto_pom.xml.j2
index 886cd02663..11869120ec 100644
--- a/hermetic_build/library_generation/owlbot/templates/poms/proto_pom.xml.j2
+++ b/hermetic_build/library_generation/owlbot/templates/poms/proto_pom.xml.j2
@@ -4,13 +4,13 @@
   <modelVersion>4.0.0</modelVersion>
   <groupId>{{module.group_id}}</groupId>
   <artifactId>{{module.artifact_id}}</artifactId>
-  <version>{{module.version}}</version><!-- {x-version-update:{{module.artifact_id}}:current} -->
+  <version>{{module.version}}</version><!-- {x-version-update:{{release_please_key}}:current} -->
   <name>{{module.artifact_id}}</name>
   <description>Proto library for {{main_module.artifact_id}}</description>
   <parent>
     <groupId>{{parent_module.group_id}}</groupId>
     <artifactId>{{parent_module.artifact_id}}</artifactId>
-    <version>{{parent_module.version}}</version><!-- {x-version-update:{{main_module.artifact_id}}:current} -->
+    <version>{{parent_module.version}}</version><!-- {x-version-update:{{release_please_key}}:current} -->
   </parent>
   <dependencies>
     <dependency>
diff --git a/hermetic_build/library_generation/tests/owlbot/fix_poms_unit_tests.py b/hermetic_build/library_generation/tests/owlbot/fix_poms_unit_tests.py
index 2e66454827..c71577d91e 100644
--- a/hermetic_build/library_generation/tests/owlbot/fix_poms_unit_tests.py
+++ b/hermetic_build/library_generation/tests/owlbot/fix_poms_unit_tests.py
@@ -14,6 +14,8 @@
 import os
 import shutil
 import unittest
+import tempfile
+from pathlib import Path
 from library_generation.owlbot.src.fix_poms import main
 from library_generation.tests.compare_poms import compare_pom_in_subdir
 
@@ -22,6 +24,14 @@
 
 
 class FixPomsTest(unittest.TestCase):
+    def setUp(self):
+        self.temp_dir = tempfile.mkdtemp()
+        self.start_dir = os.getcwd()
+        os.chdir(self.temp_dir)
+
+    def tearDown(self):
+        os.chdir(self.start_dir)
+
     def test_update_poms_group_id_does_not_start_with_google_correctly(self):
         ad_manager_resource = os.path.join(resources_dir, "java-admanager")
         versions_file = os.path.join(ad_manager_resource, "versions.txt")
@@ -35,6 +45,116 @@ def test_update_poms_group_id_does_not_start_with_google_correctly(self):
         for sub_dir in sub_dirs:
             self.__remove_file_in_subdir(ad_manager_resource, sub_dir)
 
+    def test_add_new_library(self):
+        # Setup test environment in a structure similar to a real repo
+        repo_dir = os.path.join(self.temp_dir, "google-cloud-java")
+        os.makedirs(repo_dir)
+        source_resource_dir = os.path.join(resources_dir, "google-cloud-java")
+        new_library_dir_name = "java-newapi"
+        new_library_path = os.path.join(repo_dir, new_library_dir_name)
+
+        # Copy test resources to the temporary directory
+        shutil.copytree(
+            os.path.join(source_resource_dir, "java-newapi"), new_library_path
+        )
+
+        # Modify the .repo-metadata.json in the temporary new library folder
+        repo_metadata_path = os.path.join(new_library_path, ".repo-metadata.json")
+        with open(repo_metadata_path, "r") as f:
+            repo_metadata_content = f.read()
+        repo_metadata_content = repo_metadata_content.replace(
+            "google-cloud-newfolder", "google-cloud-newapi"
+        )
+        with open(repo_metadata_path, "w") as f:
+            f.write(repo_metadata_content)
+
+        source_versions_file = os.path.join(source_resource_dir, "versions.txt")
+        dest_versions_file = os.path.join(repo_dir, "versions.txt")
+        shutil.copyfile(source_versions_file, dest_versions_file)
+
+        # Create dummy directories for proto and grpc modules.
+        # In the full generation process, `generate_library.sh` would create these.
+        os.makedirs(os.path.join(new_library_path, "proto-google-cloud-newapi-v1"))
+        os.makedirs(os.path.join(new_library_path, "grpc-google-cloud-newapi-v1"))
+        os.chdir(new_library_path)
+
+        # Get initial state of versions.txt (excluding comments and empty lines)
+        with open(dest_versions_file, "r") as f:
+            initial_active_lines = [
+                line.strip()
+                for line in f
+                if line.strip() and not line.strip().startswith("#")
+            ]
+
+        # Execute the main function from fix_poms.py
+        main(dest_versions_file, "true")
+
+        # --- Verify versions.txt ---
+        with open(dest_versions_file, "r") as f:
+            updated_versions_content = f.readlines()
+
+        updated_active_lines = [
+            line.strip()
+            for line in updated_versions_content
+            if line.strip() and not line.strip().startswith("#")
+        ]
+
+        self.assertEqual(
+            len(initial_active_lines) + 1,
+            len(updated_active_lines),
+            "A single line should have been added to versions.txt",
+        )
+
+        expected_new_line = "newapi:0.0.0:0.0.1-SNAPSHOT"
+        self.assertTrue(
+            any(expected_new_line in line for line in updated_active_lines),
+            f"The new line '{expected_new_line}' was not found in versions.txt",
+        )
+
+        filtered_updated_lines = [
+            line for line in updated_active_lines if expected_new_line not in line
+        ]
+        self.assertCountEqual(
+            initial_active_lines,
+            filtered_updated_lines,
+            "Existing lines in versions.txt should be unaffected.",
+        )
+        self.assertFalse(
+            any("google-cloud-newapi" in line for line in updated_versions_content),
+            "The artifactId 'google-cloud-newapi' should not be in versions.txt",
+        )
+
+        # --- Verify generated pom.xml files ---
+        expected_poms = [
+            "pom.xml",
+            "google-cloud-newapi/pom.xml",
+            "google-cloud-newapi-bom/pom.xml",
+            "proto-google-cloud-newapi-v1/pom.xml",
+            "grpc-google-cloud-newapi-v1/pom.xml",
+        ]
+        for pom_path in expected_poms:
+            full_pom_path = os.path.join(new_library_path, pom_path)
+            self.assertTrue(
+                os.path.exists(full_pom_path),
+                f"Expected POM file not found: {full_pom_path}",
+            )
+            with open(full_pom_path, "r") as f:
+                pom_content = f.read()
+            self.assertIn(
+                "<!-- {x-version-update:newapi:current} -->",
+                pom_content,
+                f"x-version-update tag in {pom_path} does not reference 'newapi'",
+            )
+            # Ensure the artifactId is not changed to the release_please_key
+            if pom_path == "google-cloud-newapi/pom.xml":
+                self.assertIn(
+                    "<artifactId>google-cloud-newapi</artifactId>", pom_content
+                )
+            if pom_path == "proto-google-cloud-newapi-v1/pom.xml":
+                self.assertIn(
+                    "<artifactId>proto-google-cloud-newapi-v1</artifactId>", pom_content
+                )
+
     @classmethod
     def __copy__golden(cls, base_dir: str, subdir: str):
         golden = os.path.join(base_dir, subdir, "pom-golden.xml")
diff --git a/hermetic_build/library_generation/tests/resources/test-owlbot/google-cloud-java/java-newapi/.repo-metadata.json b/hermetic_build/library_generation/tests/resources/test-owlbot/google-cloud-java/java-newapi/.repo-metadata.json
new file mode 100644
index 0000000000..5bc5879b8b
--- /dev/null
+++ b/hermetic_build/library_generation/tests/resources/test-owlbot/google-cloud-java/java-newapi/.repo-metadata.json
@@ -0,0 +1,16 @@
+{
+  "api_shortname": "newapi",
+  "name_pretty": "Google New API for Test",
+  "product_documentation": "https://developers.google.com/",
+  "api_description": "The Ad Manager API enables an app to integrate with Google Ad Manager. You can read Ad Manager data and run reports using the API.",
+  "client_documentation": "https://cloud.google.com/java/docs/reference/ad-manager/latest/overview",
+  "release_level": "preview",
+  "transport": "http",
+  "language": "java",
+  "repo": "googleapis/google-cloud-java",
+  "repo_short": "java-newapi",
+  "distribution_name": "com.google.cloud:google-cloud-newapi",
+  "api_id": "newapi.googleapis.com",
+  "library_type": "GAPIC_AUTO",
+  "requires_billing": true
+}
diff --git a/hermetic_build/library_generation/tests/resources/test-owlbot/google-cloud-java/versions.txt b/hermetic_build/library_generation/tests/resources/test-owlbot/google-cloud-java/versions.txt
new file mode 100644
index 0000000000..4424aed41e
--- /dev/null
+++ b/hermetic_build/library_generation/tests/resources/test-owlbot/google-cloud-java/versions.txt
@@ -0,0 +1,7 @@
+# Format:
+# module:released-version:current-version
+
+google-cloud-java:1.36.0:1.37.0-SNAPSHOT
+ad-manager:0.1.0:0.2.0-SNAPSHOT
+proto-ad-manager-v1:0.1.0:0.2.0-SNAPSHOT
+java-ad-manager:0.1.0:0.2.0-SNAPSHOT
diff --git a/hermetic_build/library_generation/tests/resources/test-owlbot/java-admanager/versions.txt b/hermetic_build/library_generation/tests/resources/test-owlbot/java-admanager/versions.txt
index 3f073728f3..930a79a07e 100644
--- a/hermetic_build/library_generation/tests/resources/test-owlbot/java-admanager/versions.txt
+++ b/hermetic_build/library_generation/tests/resources/test-owlbot/java-admanager/versions.txt
@@ -1,6 +1,7 @@
 # Format:
 # module:released-version:current-version
 
+admanager:0.0.0:0.0.1-SNAPSHOT
 google-cloud-java:1.36.0:1.37.0-SNAPSHOT
-ad-manager:0.1.0:0.2.0-SNAPSHOT
 proto-ad-manager-v1:0.1.0:0.2.0-SNAPSHOT
+ad-manager:0.1.0:0.2.0-SNAPSHOT