diff --git a/cumulus_etl/__init__.py b/cumulus_etl/__init__.py
index 05fb822..4845145 100644
--- a/cumulus_etl/__init__.py
+++ b/cumulus_etl/__init__.py
@@ -1,3 +1,3 @@
 """Turns FHIR data into de-identified & aggregated records"""
 
-__version__ = "1.3.0"
+__version__ = "1.4.0"
diff --git a/cumulus_etl/formats/deltalake.py b/cumulus_etl/formats/deltalake.py
index 06aa286..6125cec 100644
--- a/cumulus_etl/formats/deltalake.py
+++ b/cumulus_etl/formats/deltalake.py
@@ -101,6 +101,7 @@ def update_delta_table(
         table = (
             delta.DeltaTable.createIfNotExists(self.spark)
             .addColumns(updates.schema)
+            .clusterBy(*self.uniqueness_fields)
             .location(self._table_path(self.dbname))
             .execute()
         )
diff --git a/pyproject.toml b/pyproject.toml
index 4a303aa..9ddbb25 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -13,7 +13,7 @@ requires-python = ">= 3.10"
 dependencies = [
     "ctakesclient >= 5.1, < 6",
     "cumulus-fhir-support >= 1.2, < 2",
-    "delta-spark >= 3, < 4",
+    "delta-spark >= 3.2.1, < 4",
     "httpx < 1",
     "inscriptis < 3",
     "jwcrypto < 2",
diff --git a/tests/etl/test_etl_cli.py b/tests/etl/test_etl_cli.py
index c057927..9bd5bcd 100644
--- a/tests/etl/test_etl_cli.py
+++ b/tests/etl/test_etl_cli.py
@@ -410,20 +410,24 @@ async def test_etl_job_deltalake(self):
                 "_delta_log/.00000000000000000000.json.crc",
                 "_delta_log/00000000000000000001.json",  # merge
                 "_delta_log/.00000000000000000001.json.crc",
-                "_delta_log/00000000000000000002.json",  # vacuum start
+                "_delta_log/00000000000000000002.json",  # optimize
                 "_delta_log/.00000000000000000002.json.crc",
-                "_delta_log/00000000000000000003.json",  # vacuum end
+                "_delta_log/00000000000000000003.json",  # vacuum start
                 "_delta_log/.00000000000000000003.json.crc",
+                "_delta_log/00000000000000000004.json",  # vacuum end
+                "_delta_log/.00000000000000000004.json.crc",
                 "_symlink_format_manifest/manifest",
                 "_symlink_format_manifest/.manifest.crc",
             },
             metadata_files,
         )
 
-        self.assertEqual(1, len(data_files))
+        # Expect two data files - one will be original (now marked as deleted from optimize call)
+        # and the other will be the new optimized file.
+        self.assertEqual(2, len(data_files))
         self.assertRegex(data_files.pop(), r"part-00000-.*-c000.snappy.parquet")
 
-        self.assertEqual(1, len(data_crc_files))
+        self.assertEqual(2, len(data_crc_files))
         self.assertRegex(data_crc_files.pop(), r".part-00000-.*-c000.snappy.parquet.crc")