diff --git a/packages/google-cloud-storage/google/cloud/storage/_bucket_metadata_cache.py b/packages/google-cloud-storage/google/cloud/storage/_bucket_metadata_cache.py
new file mode 100644
index 000000000000..02634f39fc98
--- /dev/null
+++ b/packages/google-cloud-storage/google/cloud/storage/_bucket_metadata_cache.py
@@ -0,0 +1,149 @@
+# 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.
+
+"""In-memory LRU cache for bucket metadata supporting App-centric Observability (ACO)."""
+
+import logging
+import threading
+
+from google.api_core import exceptions as api_exceptions
+from google.cloud.exceptions import NotFound
+from google.cloud.storage._lru_cache import LRUCache
+
+logger = logging.getLogger(__name__)
+
+
+class BucketMetadataCache:
+    """Thread-safe LRU cache for storing GCS bucket metadata (project number and location).
+
+    Supports Singleflight asynchronous background fetching to prevent stampedes on cache misses.
+    """
+
+    def __init__(self, client, max_size=10000):
+        self._client = client
+        self._cache = LRUCache(max_size)
+        self._lock = threading.Lock()
+        self._inflight_fetches = set()
+        self._inflight_checks = set()
+
+    def get(self, bucket_name):
+        """Thread-safely retrieve cached metadata without queueing fetch."""
+        with self._lock:
+            return self._cache.get(bucket_name)
+
+    def get_or_queue_fetch(self, bucket_name):
+        """Retrieve bucket metadata or queue a background fetch on cache miss.
+
+        Returns None immediately on cache miss so caller does not block.
+        """
+        with self._lock:
+            if bucket_name in self._cache:
+                return self._cache.get(bucket_name)
+            elif bucket_name in self._inflight_fetches:
+                # this would be the case of thundering herd, where 'n' threads
+                # all of them faced "cache miss" and 1 is in progress to fetch metadata.
+                # hence we don't want rest `n - 1` threads to make the same req
+                return None
+            else:
+                # fire a background thread and get bucket metadata.
+                self._inflight_fetches.add(bucket_name)
+                threading.Thread(
+                    target=self._fetch_background, args=(bucket_name,), daemon=True
+                ).start()
+                return None
+
+    def check_and_evict(self, bucket_name):
+        """Asynchronously verify if a bucket exists on 404 and evict if deleted."""
+        with self._lock:
+            if bucket_name not in self._cache:
+                return
+            if bucket_name in self._inflight_checks:
+                return
+            self._inflight_checks.add(bucket_name)
+            threading.Thread(
+                target=self._verify_existence_background,
+                args=(bucket_name,),
+                daemon=True,
+            ).start()
+
+    def _verify_existence_background(self, bucket_name):
+        try:
+            bucket = self._client.bucket(bucket_name)
+            if not bucket.exists():
+                self.evict(bucket_name)
+        except Exception as e:
+            logger.debug(
+                f"Background verification for bucket existence failed for {bucket_name}: {e}"
+            )
+        finally:
+            with self._lock:
+                self._inflight_checks.discard(bucket_name)
+
+    def _fetch_background(self, bucket_name):
+        """Asynchronously fetch bucket metadata and update the cache."""
+        try:
+            bucket = self._client.get_bucket(bucket_name, timeout=10.0)
+            self.update_from_bucket(bucket)
+        except (NotFound, api_exceptions.NotFound):
+            self.evict(bucket_name)
+        except api_exceptions.Forbidden:
+            # On 403 (Forbidden), cache fallback values permanently to avoid retry storms
+            self.update_cache(
+                bucket_name, f"projects/_/buckets/{bucket_name}", "global"
+            )
+        except Exception as e:
+            logger.debug(
+                f"Background fetch for bucket metadata failed for {bucket_name}: {e}"
+            )
+        finally:
+            with self._lock:
+                self._inflight_fetches.discard(bucket_name)
+
+    def update_from_bucket(self, bucket):
+        """Update cache from a Bucket instance."""
+        if not bucket or not bucket.name:
+            return
+
+        project_number = getattr(bucket, "project_number", None)
+        location = getattr(bucket, "location", None) or "global"
+        location = location.lower()
+        location_type = getattr(bucket, "location_type", None) or "region"
+        location_type = location_type.lower()
+
+        if location_type in ("multi-region", "dual-region"):
+            location = "global"
+
+        if project_number:
+            destination_id = f"projects/{project_number}/buckets/{bucket.name}"
+        else:
+            destination_id = f"projects/_/buckets/{bucket.name}"
+
+        self.update_cache(bucket.name, destination_id, location)
+
+    def update_cache(self, bucket_name, destination_id, location):
+        """Thread-safely update or insert a cache entry with bounded size."""
+        with self._lock:
+            self._cache.put(bucket_name, (destination_id, location))
+
+    def evict(self, bucket_name):
+        """Remove a bucket from the cache (e.g., on 404)."""
+        with self._lock:
+            self._cache.delete(bucket_name)
+
+    def clear(self):
+        """Clear all cached metadata."""
+        with self._lock:
+            self._cache.clear()
+            self._inflight_fetches.clear()
+            self._inflight_checks.clear()
diff --git a/packages/google-cloud-storage/google/cloud/storage/_lru_cache.py b/packages/google-cloud-storage/google/cloud/storage/_lru_cache.py
new file mode 100644
index 000000000000..23a37cf846d3
--- /dev/null
+++ b/packages/google-cloud-storage/google/cloud/storage/_lru_cache.py
@@ -0,0 +1,89 @@
+# 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.
+
+"""A Least Recently Used (LRU) cache implementation."""
+
+from collections import OrderedDict
+from typing import Generic, Optional, TypeVar
+
+K = TypeVar("K")
+V = TypeVar("V")
+
+
+class LRUCache(Generic[K, V]):
+    """A Least Recently Used (LRU) cache implementation using OrderedDict.
+
+    :type capacity: int
+    :param capacity: The maximum number of items the cache can hold.
+    """
+
+    def __init__(self, capacity: int) -> None:
+        if capacity <= 0:
+            raise ValueError("Capacity must be greater than 0")
+        self._capacity = capacity
+        self._cache: OrderedDict[K, V] = OrderedDict()
+
+    @property
+    def capacity(self) -> int:
+        """Return the capacity of the cache."""
+        return self._capacity
+
+    def get(self, key: K, default: Optional[V] = None) -> Optional[V]:
+        """Retrieve an item from the cache.
+
+        If the key exists, it is moved to the end (marked as most recently used).
+
+        :type key: Any
+        :param key: The key to look up in the cache.
+
+        :type default: Any
+        :param default: Default value to return if key is not found.
+        """
+        if key not in self._cache:
+            return default
+        self._cache.move_to_end(key)
+        return self._cache[key]
+
+    def put(self, key: K, value: V) -> None:
+        """Add or update an item in the cache.
+
+        If the key already exists, it is updated and moved to the end.
+        If adding the item exceeds capacity, the least recently used item (at the beginning)
+        is evicted.
+
+        :type key: Any
+        :param key: The key to store.
+
+        :type value: Any
+        :param value: The value to store.
+        """
+        if key in self._cache:
+            self._cache.move_to_end(key)
+        self._cache[key] = value
+        if len(self._cache) > self._capacity:
+            self._cache.popitem(last=False)
+
+    def __len__(self) -> int:
+        return len(self._cache)
+
+    def __contains__(self, key: K) -> bool:
+        return key in self._cache
+
+    def clear(self) -> None:
+        """Clear all items from the cache."""
+        self._cache.clear()
+
+    def delete(self, key: K) -> None:
+        """Remove an item from the cache if it exists."""
+        self._cache.pop(key, None)
diff --git a/packages/google-cloud-storage/tests/unit/test__bucket_metadata_cache.py b/packages/google-cloud-storage/tests/unit/test__bucket_metadata_cache.py
new file mode 100644
index 000000000000..39f6975ded4c
--- /dev/null
+++ b/packages/google-cloud-storage/tests/unit/test__bucket_metadata_cache.py
@@ -0,0 +1,203 @@
+# 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.
+
+import unittest
+from unittest import mock
+
+from google.api_core import exceptions as api_exceptions
+from google.cloud.exceptions import NotFound
+from google.cloud.storage._bucket_metadata_cache import BucketMetadataCache
+
+
+class TestBucketMetadataCache(unittest.TestCase):
+    @mock.patch("threading.Thread")
+    def test_lru_eviction(self, mock_thread):
+        client = mock.Mock()
+        cache = BucketMetadataCache(client, max_size=3)
+
+        cache.update_cache("b1", "dest1", "loc1")
+        cache.update_cache("b2", "dest2", "loc2")
+        cache.update_cache("b3", "dest3", "loc3")
+        cache.update_cache("b4", "dest4", "loc4")  # Evicts b1 (oldest)
+
+        self.assertIsNone(cache.get_or_queue_fetch("b1"))
+        self.assertEqual(cache.get_or_queue_fetch("b2"), ("dest2", "loc2"))
+        self.assertEqual(cache.get_or_queue_fetch("b3"), ("dest3", "loc3"))
+        self.assertEqual(cache.get_or_queue_fetch("b4"), ("dest4", "loc4"))
+
+    def test_update_from_bucket(self):
+        client = mock.Mock()
+        cache = BucketMetadataCache(client)
+
+        # Multi-region -> global
+        b1 = mock.Mock()
+        b1.name = "b1"
+        b1.location = "US"
+        b1.location_type = "multi-region"
+        b1.project_number = 123
+        cache.update_from_bucket(b1)
+        self.assertEqual(
+            cache.get_or_queue_fetch("b1"), ("projects/123/buckets/b1", "global")
+        )
+
+        # Dual-region -> global
+        b2 = mock.Mock()
+        b2.name = "b2"
+        b2.location = "NAM4"
+        b2.location_type = "dual-region"
+        b2.project_number = 456
+        cache.update_from_bucket(b2)
+        self.assertEqual(
+            cache.get_or_queue_fetch("b2"), ("projects/456/buckets/b2", "global")
+        )
+
+        # Region -> us-east1
+        b3 = mock.Mock()
+        b3.name = "b3"
+        b3.location = "US-EAST1"
+        b3.location_type = "region"
+        b3.project_number = 789
+        cache.update_from_bucket(b3)
+        self.assertEqual(
+            cache.get_or_queue_fetch("b3"), ("projects/789/buckets/b3", "us-east1")
+        )
+
+        # Missing project number -> _
+        b4 = mock.Mock()
+        b4.name = "b4"
+        b4.location = "eu-west1"
+        b4.location_type = "region"
+        b4.project_number = None
+        cache.update_from_bucket(b4)
+        self.assertEqual(
+            cache.get_or_queue_fetch("b4"), ("projects/_/buckets/b4", "eu-west1")
+        )
+
+    @mock.patch("threading.Thread")
+    def test_get_or_queue_fetch(self, mock_thread):
+        client = mock.Mock()
+        cache = BucketMetadataCache(client)
+
+        # Cache miss -> returns None immediately and spawns thread
+        result = cache.get_or_queue_fetch("my-bucket")
+        self.assertIsNone(result)
+        mock_thread.assert_called_once()
+
+        # Second immediate lookup -> returns None, does not spawn another thread (singleflight)
+        mock_thread.reset_mock()
+        result2 = cache.get_or_queue_fetch("my-bucket")
+        self.assertIsNone(result2)
+        mock_thread.assert_not_called()
+
+    def test_fetch_background_success(self):
+        client = mock.Mock()
+        b1 = mock.Mock()
+        b1.name = "b1"
+        b1.location = "US-WEST1"
+        b1.location_type = "region"
+        b1.project_number = 999
+        client.get_bucket.return_value = b1
+
+        cache = BucketMetadataCache(client)
+        cache._inflight_fetches.add("b1")
+
+        cache._fetch_background("b1")
+
+        self.assertEqual(
+            cache.get_or_queue_fetch("b1"), ("projects/999/buckets/b1", "us-west1")
+        )
+        self.assertNotIn("b1", cache._inflight_fetches)
+
+    def test_fetch_background_not_found(self):
+        client = mock.Mock()
+        client.get_bucket.side_effect = NotFound("Bucket not found")
+        cache = BucketMetadataCache(client)
+        cache.update_cache("b1", "projects/_/buckets/b1", "global")
+        cache._inflight_fetches.add("b1")
+
+        cache._fetch_background("b1")
+
+        self.assertNotIn("b1", cache._cache)
+        self.assertNotIn("b1", cache._inflight_fetches)
+
+    def test_fetch_background_forbidden(self):
+        client = mock.Mock()
+        client.get_bucket.side_effect = api_exceptions.Forbidden("403")
+        cache = BucketMetadataCache(client)
+        cache._inflight_fetches.add("b1")
+
+        cache._fetch_background("b1")
+
+        self.assertEqual(
+            cache.get_or_queue_fetch("b1"), ("projects/_/buckets/b1", "global")
+        )
+        self.assertNotIn("b1", cache._inflight_fetches)
+
+    @mock.patch("threading.Thread")
+    def test_clear_and_evict(self, mock_thread):
+        client = mock.Mock()
+        cache = BucketMetadataCache(client)
+
+        cache.update_cache("b1", "dest1", "loc1")
+        cache.evict("b1")
+        self.assertNotIn("b1", cache._cache)
+
+        cache.update_cache("b2", "dest2", "loc2")
+        cache.clear()
+        self.assertNotIn("b2", cache._cache)
+
+    @mock.patch("threading.Thread")
+    def test_check_and_evict_queue(self, mock_thread):
+        client = mock.Mock()
+        cache = BucketMetadataCache(client)
+        cache.update_cache("b1", "dest1", "loc1")
+
+        cache.check_and_evict("b1")
+        mock_thread.assert_called_once()
+        self.assertIn("b1", cache._inflight_checks)
+
+        # Second immediate check -> singleflight
+        mock_thread.reset_mock()
+        cache.check_and_evict("b1")
+        mock_thread.assert_not_called()
+
+    def test_verify_existence_background_exists(self):
+        client = mock.Mock()
+        b1 = mock.Mock()
+        b1.exists.return_value = True
+        client.bucket.return_value = b1
+
+        cache = BucketMetadataCache(client)
+        cache.update_cache("b1", "dest1", "loc1")
+        cache._inflight_checks.add("b1")
+
+        cache._verify_existence_background("b1")
+
+        self.assertIn("b1", cache._cache)
+        self.assertNotIn("b1", cache._inflight_checks)
+
+    def test_verify_existence_background_deleted(self):
+        client = mock.Mock()
+        b1 = mock.Mock()
+        b1.exists.return_value = False
+        client.bucket.return_value = b1
+
+        cache = BucketMetadataCache(client)
+        cache.update_cache("b1", "dest1", "loc1")
+        cache._inflight_checks.add("b1")
+
+        cache._verify_existence_background("b1")
+
+        self.assertNotIn("b1", cache._cache)
+        self.assertNotIn("b1", cache._inflight_checks)
diff --git a/packages/google-cloud-storage/tests/unit/test__lru_cache.py b/packages/google-cloud-storage/tests/unit/test__lru_cache.py
new file mode 100644
index 000000000000..62b612be5513
--- /dev/null
+++ b/packages/google-cloud-storage/tests/unit/test__lru_cache.py
@@ -0,0 +1,101 @@
+# 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.
+
+import pytest
+
+from google.cloud.storage._lru_cache import LRUCache
+
+
+def test_lru_cache_capacity():
+    cache = LRUCache(capacity=3)
+    assert cache.capacity == 3
+
+    with pytest.raises(ValueError):
+        LRUCache(capacity=0)
+
+    with pytest.raises(ValueError):
+        LRUCache(capacity=-1)
+
+
+def test_lru_cache_put_and_get():
+    cache = LRUCache(capacity=2)
+    assert cache.get("a") is None
+    assert cache.get("a", default="default") == "default"
+
+    cache.put("a", 1)
+    assert cache.get("a") == 1
+    assert len(cache) == 1
+    assert "a" in cache
+
+    cache.put("b", 2)
+    assert cache.get("b") == 2
+    assert len(cache) == 2
+    assert "b" in cache
+
+
+def test_lru_cache_eviction():
+    cache = LRUCache(capacity=2)
+    cache.put("a", 1)
+    cache.put("b", 2)
+
+    # Access "a" so "b" becomes least recently used
+    assert cache.get("a") == 1
+
+    # Put "c" should evict "b"
+    cache.put("c", 3)
+
+    assert "b" not in cache
+    assert cache.get("b") is None
+    assert cache.get("a") == 1
+    assert cache.get("c") == 3
+    assert len(cache) == 2
+
+
+def test_lru_cache_update():
+    cache = LRUCache(capacity=2)
+    cache.put("a", 1)
+    cache.put("b", 2)
+
+    # Update "a", so it becomes most recently used
+    cache.put("a", 10)
+
+    # Put "c" should evict "b"
+    cache.put("c", 3)
+
+    assert "b" not in cache
+    assert cache.get("a") == 10
+    assert cache.get("c") == 3
+
+
+def test_lru_cache_clear():
+    cache = LRUCache(capacity=2)
+    cache.put("a", 1)
+    cache.put("b", 2)
+
+    cache.clear()
+    assert len(cache) == 0
+    assert "a" not in cache
+    assert "b" not in cache
+
+
+def test_lru_cache_delete():
+    cache = LRUCache(capacity=2)
+    cache.put("a", 1)
+    cache.put("b", 2)
+
+    cache.delete("a")
+    assert len(cache) == 1
+    assert "a" not in cache
+    assert cache.get("a") is None
+    assert cache.get("b") == 2