diff --git a/src/apify_client/_resource_clients/dataset.py b/src/apify_client/_resource_clients/dataset.py
index 1f772dde..7cb3b399 100644
--- a/src/apify_client/_resource_clients/dataset.py
+++ b/src/apify_client/_resource_clients/dataset.py
@@ -402,6 +402,7 @@ def stream_items(
         skip_hidden: bool | None = None,
         xml_root: str | None = None,
         xml_row: str | None = None,
+        flatten: list[str] | None = None,
         signature: str | None = None,
         timeout: Timeout = 'long',
     ) -> Iterator[HttpResponse]:
@@ -445,6 +446,7 @@ def stream_items(
             xml_root: Overrides default root element name of xml output. By default the root element is items.
             xml_row: Overrides default element name that wraps each page or page function result object in xml output.
                 By default the element name is item.
+            flatten: A list of fields that should be flattened.
             signature: Signature used to access the items.
             timeout: Timeout for the API HTTP request.
 
@@ -469,6 +471,7 @@ def stream_items(
                 skipHidden=skip_hidden,
                 xmlRoot=xml_root,
                 xmlRow=xml_row,
+                flatten=flatten,
                 signature=signature,
             )
 
@@ -964,6 +967,7 @@ async def stream_items(
         skip_hidden: bool | None = None,
         xml_root: str | None = None,
         xml_row: str | None = None,
+        flatten: list[str] | None = None,
         signature: str | None = None,
         timeout: Timeout = 'long',
     ) -> AsyncIterator[HttpResponse]:
@@ -1007,6 +1011,7 @@ async def stream_items(
             xml_root: Overrides default root element name of xml output. By default the root element is items.
             xml_row: Overrides default element name that wraps each page or page function result object in xml output.
                 By default the element name is item.
+            flatten: A list of fields that should be flattened.
             signature: Signature used to access the items.
             timeout: Timeout for the API HTTP request.
 
@@ -1031,6 +1036,7 @@ async def stream_items(
                 skipHidden=skip_hidden,
                 xmlRoot=xml_root,
                 xmlRow=xml_row,
+                flatten=flatten,
                 signature=signature,
             )
 
diff --git a/tests/unit/test_client_streaming.py b/tests/unit/test_client_streaming.py
index 9e5782e7..811fda7d 100644
--- a/tests/unit/test_client_streaming.py
+++ b/tests/unit/test_client_streaming.py
@@ -53,6 +53,28 @@ async def test_dataset_stream_items_async(
         assert await response.aread() == STREAM_CONTENT
 
 
+def test_dataset_stream_items_flatten_sync(httpserver: HTTPServer) -> None:
+    """`flatten` is sent as a comma-separated query parameter."""
+    httpserver.expect_request(
+        f'/v2/datasets/{DATASET_ID}/items', query_string={'format': 'json', 'flatten': 'a,b.c'}
+    ).respond_with_data(STREAM_CONTENT)
+    client = ApifyClient(token='test', api_url=httpserver.url_for('/').removesuffix('/'))
+
+    with client.dataset(DATASET_ID).stream_items(flatten=['a', 'b.c']) as response:
+        assert response.read() == STREAM_CONTENT
+
+
+async def test_dataset_stream_items_flatten_async(httpserver: HTTPServer) -> None:
+    """`flatten` is sent as a comma-separated query parameter."""
+    httpserver.expect_request(
+        f'/v2/datasets/{DATASET_ID}/items', query_string={'format': 'json', 'flatten': 'a,b.c'}
+    ).respond_with_data(STREAM_CONTENT)
+    client = ApifyClientAsync(token='test', api_url=httpserver.url_for('/').removesuffix('/'))
+
+    async with client.dataset(DATASET_ID).stream_items(flatten=['a', 'b.c']) as response:
+        assert await response.aread() == STREAM_CONTENT
+
+
 def test_key_value_store_stream_record_sync(
     httpserver: HTTPServer,
     http_client_class: type[HttpClient],