diff --git a/unstract/connectors/src/unstract/connectors/filesystems/google_cloud_storage/google_cloud_storage.py b/unstract/connectors/src/unstract/connectors/filesystems/google_cloud_storage/google_cloud_storage.py
index 63f174feb9..e96a21d0c3 100644
--- a/unstract/connectors/src/unstract/connectors/filesystems/google_cloud_storage/google_cloud_storage.py
+++ b/unstract/connectors/src/unstract/connectors/filesystems/google_cloud_storage/google_cloud_storage.py
@@ -255,7 +255,7 @@ def extract_modified_date(self, metadata: dict[str, Any]) -> datetime | None:
         return None
 
     def test_credentials(self) -> bool:
-        """Test Google Cloud Storage credentials by accessing the root path info.
+        """Test Google Cloud Storage credentials by listing the project's buckets.
 
         Raises:
             ConnectorError: connector-error
@@ -264,7 +264,11 @@ def test_credentials(self) -> bool:
             boolean: true if test-connection is successful
         """
         try:
-            self.get_fsspec_fs().info("/")
+            # `ls("")` lists buckets with the configured project. Do not use
+            # `info("/")`: from gcsfs 2026.x it sends `GET b/` without the
+            # project, which GCS rejects with "Required parameter: project"
+            # for every connector (UN-4224).
+            self.get_fsspec_fs().ls("")
         except Exception as e:
             error_msg = (
                 "Error from Google Cloud Storage while testing connection. \n"
diff --git a/unstract/connectors/tests/filesystems/test_google_cloud_storage_fs.py b/unstract/connectors/tests/filesystems/test_google_cloud_storage_fs.py
new file mode 100644
index 0000000000..fb8827fe17
--- /dev/null
+++ b/unstract/connectors/tests/filesystems/test_google_cloud_storage_fs.py
@@ -0,0 +1,69 @@
+"""GCS connector test-connection request shape (UN-4224).
+
+From gcsfs 2026.x, ``info("/")`` sends ``GET b/`` without the project, which
+GCS rejects with ``Required parameter: project`` (400) for every connector.
+Test connection must list buckets with the configured project instead — the
+same request gcsfs 2024.x sent for ``info("/")``.
+"""
+
+from typing import Any
+
+import pytest
+from gcsfs import core as gcsfs_core
+
+# The core class explicitly: production runs it (storage_compat keeps gcsfs off
+# the experimental ExtendedGcsFileSystem), and `gcsfs.GCSFileSystem` would
+# depend on whether gcsfs was imported before storage_compat in this process.
+from gcsfs.core import GCSFileSystem
+
+from unstract.connectors.filesystems.google_cloud_storage.google_cloud_storage import (
+    GoogleCloudStorageFS,
+)
+
+_Calls = list[tuple[str, str, dict[str, Any]]]
+
+
+@pytest.fixture
+def gcs_requests(monkeypatch: pytest.MonkeyPatch) -> _Calls:
+    """Record gcsfs API requests and answer the way GCS does."""
+    calls: _Calls = []
+
+    async def fake_call(
+        self: GCSFileSystem, method: str, path: str, *args: Any, **kwargs: Any
+    ) -> dict[str, Any]:
+        calls.append((method, path, kwargs))
+        if path.rstrip("/") == "b" and "project" not in kwargs:
+            # What GCS answers for a bucket listing that carries no project.
+            raise gcsfs_core.HttpError(
+                {"code": 400, "message": "Required parameter: project"}
+            )
+        return {"kind": "storage#buckets", "items": [{"name": "bucket-a"}]}
+
+    monkeypatch.setattr(gcsfs_core.GCSFileSystem, "_call", fake_call)
+    return calls
+
+
+def _connector(project: str) -> GoogleCloudStorageFS:
+    connector = GoogleCloudStorageFS({"project_id": project, "json_credentials": "{}"})
+    # Bypass the lazy credential-backed client; only the request shape matters.
+    connector._gcs_fs = GCSFileSystem(
+        token="anon", project=project, skip_instance_cache=True
+    )
+    return connector
+
+
+def test_test_credentials_lists_buckets_with_the_configured_project(
+    gcs_requests: _Calls,
+) -> None:
+    assert _connector("my-project").test_credentials() is True
+
+    assert gcs_requests, "test_credentials made no request"
+    method, path, kwargs = gcs_requests[0]
+    assert (method, path) == ("GET", "b")
+    assert kwargs.get("project") == "my-project"
+    assert not any(c[1] == "b/" for c in gcs_requests), "sent the project-less GET b/"
+
+
+def test_uses_the_core_gcsfs_class() -> None:
+    assert type(_connector("my-project")._gcs_fs) is GCSFileSystem
+    assert GCSFileSystem.__module__ == "gcsfs.core"