diff --git a/moto/s3/models.py b/moto/s3/models.py
index c0f11809b..68e188fec 100644
--- a/moto/s3/models.py
+++ b/moto/s3/models.py
@@ -351,11 +351,12 @@ class FakeKey(BaseModel, ManagedState):
 
 
 class FakeMultipart(BaseModel):
-    def __init__(self, key_name, metadata, storage=None, tags=None):
+    def __init__(self, key_name, metadata, storage=None, tags=None, acl=None):
         self.key_name = key_name
         self.metadata = metadata
         self.storage = storage
         self.tags = tags
+        self.acl = acl
         self.parts = {}
         self.partlist = []  # ordered list of part ID's
         rand_b64 = base64.b64encode(os.urandom(UPLOAD_ID_BYTES))
@@ -1881,13 +1882,6 @@ class S3Backend(BaseBackend, CloudWatchMetricProvider):
             pub_block_config.get("RestrictPublicBuckets"),
         )
 
-    def initiate_multipart(self, bucket_name, key_name, metadata):
-        bucket = self.get_bucket(bucket_name)
-        new_multipart = FakeMultipart(key_name, metadata)
-        bucket.multiparts[new_multipart.id] = new_multipart
-
-        return new_multipart
-
     def complete_multipart(self, bucket_name, multipart_id, body):
         bucket = self.get_bucket(bucket_name)
         multipart = bucket.multiparts[multipart_id]
@@ -1924,9 +1918,11 @@ class S3Backend(BaseBackend, CloudWatchMetricProvider):
         return len(bucket.multiparts[multipart_id].parts) > next_part_number_marker
 
     def create_multipart_upload(
-        self, bucket_name, key_name, metadata, storage_type, tags
+        self, bucket_name, key_name, metadata, storage_type, tags, acl
     ):
-        multipart = FakeMultipart(key_name, metadata, storage=storage_type, tags=tags)
+        multipart = FakeMultipart(
+            key_name, metadata, storage=storage_type, tags=tags, acl=acl
+        )
 
         bucket = self.get_bucket(bucket_name)
         bucket.multiparts[multipart.id] = multipart
diff --git a/moto/s3/responses.py b/moto/s3/responses.py
index 64fc2e181..6d88bae44 100644
--- a/moto/s3/responses.py
+++ b/moto/s3/responses.py
@@ -1917,8 +1917,9 @@ class S3Response(BaseResponse):
             metadata = metadata_from_headers(request.headers)
             tagging = self._tagging_from_headers(request.headers)
             storage_type = request.headers.get("x-amz-storage-class", "STANDARD")
+            acl = self._acl_from_headers(request.headers)
             multipart_id = self.backend.create_multipart_upload(
-                bucket_name, key_name, metadata, storage_type, tagging
+                bucket_name, key_name, metadata, storage_type, tagging, acl
             )
 
             template = self.response_template(S3_MULTIPART_INITIATE_RESPONSE)
@@ -1947,6 +1948,7 @@ class S3Response(BaseResponse):
             )
             key.set_metadata(multipart.metadata)
             self.backend.set_key_tags(key, multipart.tags)
+            self.backend.put_object_acl(bucket_name, key.name, multipart.acl)
 
             template = self.response_template(S3_MULTIPART_COMPLETE_RESPONSE)
             headers = {}
diff --git a/tests/test_s3/test_s3_multipart.py b/tests/test_s3/test_s3_multipart.py
index 3af3ecafb..d8a0fd82c 100644
--- a/tests/test_s3/test_s3_multipart.py
+++ b/tests/test_s3/test_s3_multipart.py
@@ -193,29 +193,48 @@ def test_multipart_upload_out_of_order():
 def test_multipart_upload_with_headers():
     s3 = boto3.resource("s3", region_name=DEFAULT_REGION_NAME)
     client = boto3.client("s3", region_name=DEFAULT_REGION_NAME)
-    s3.create_bucket(Bucket="foobar")
+    bucket_name = "fancymultiparttest"
+    key_name = "the-key"
+    s3.create_bucket(Bucket=bucket_name)
 
     part1 = b"0" * REDUCED_PART_SIZE
     mp = client.create_multipart_upload(
-        Bucket="foobar", Key="the-key", Metadata={"meta": "data"}
+        Bucket=bucket_name,
+        Key=key_name,
+        Metadata={"meta": "data"},
+        StorageClass="STANDARD_IA",
+        ACL="authenticated-read",
     )
     up1 = client.upload_part(
         Body=BytesIO(part1),
         PartNumber=1,
-        Bucket="foobar",
-        Key="the-key",
+        Bucket=bucket_name,
+        Key=key_name,
         UploadId=mp["UploadId"],
     )
 
     client.complete_multipart_upload(
-        Bucket="foobar",
-        Key="the-key",
+        Bucket=bucket_name,
+        Key=key_name,
         MultipartUpload={"Parts": [{"ETag": up1["ETag"], "PartNumber": 1}]},
         UploadId=mp["UploadId"],
     )
     # we should get both parts as the key contents
-    response = client.get_object(Bucket="foobar", Key="the-key")
+    response = client.get_object(Bucket=bucket_name, Key=key_name)
     response["Metadata"].should.equal({"meta": "data"})
+    response["StorageClass"].should.equal("STANDARD_IA")
+
+    grants = client.get_object_acl(Bucket=bucket_name, Key=key_name)["Grants"]
+    grants.should.have.length_of(2)
+    grants.should.contain(
+        {
+            "Grantee": {
+                "Type": "Group",
+                "URI": "http://acs.amazonaws.com/groups/global/AuthenticatedUsers",
+            },
+            "Permission": "READ",
+        }
+    )
 
 
 @pytest.mark.parametrize(