diff --git a/CHANGELOG.md b/CHANGELOG.md
index 99ce0f3..cdbebde 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -19,5 +19,5 @@ All notable changes to this project will be documented in this file.
 ## [0.1.0] - 2026-03-09
 ### Added
 - Initial release of the Python SDK for the Altertable Lakehouse API.
-- Implemented `append`, `upload`, `query`, `query_all`, `validate`, `get_query`, and `cancel_query` methods.
+- Implemented `append`, `upsert`, `query`, `query_all`, `validate`, `get_query`, and `cancel_query` methods.
 - Full typing support with `pydantic` models.
diff --git a/README.md b/README.md
index e4c329a..bd085a9 100644
--- a/README.md
+++ b/README.md
@@ -58,18 +58,17 @@ if res.task_id:
     print(task.status)
 ```
 
-### Upload
+### Upsert
 
 ```python
-from altertable_lakehouse.models import UploadFormat, UploadMode
+from altertable_lakehouse.models import UpsertMode
 
 with open("data.csv", "rb") as f:
-    client.upload(
+    client.upsert(
         catalog="my_cat", 
         schema="my_schema", 
         table="my_table", 
-        format=UploadFormat.CSV, 
-        mode=UploadMode.APPEND, 
+        mode=UpsertMode.APPEND, 
         content=f.read()
     )
 ```
diff --git a/src/altertable_lakehouse/client.py b/src/altertable_lakehouse/client.py
index 1a5aed4..8f17153 100644
--- a/src/altertable_lakehouse/client.py
+++ b/src/altertable_lakehouse/client.py
@@ -16,8 +16,7 @@
     ValidateResponse,
     AutocompleteRequest,
     AutocompleteResponse,
-    UploadFormat,
-    UploadMode,
+    UpsertMode,
     QueryMetadata,
     QueryResult,
 )
@@ -119,31 +118,29 @@ def get_task(self, task_id: str) -> TaskResponse:
         except httpx.RequestError as e:
             self._handle_error(e)
 
-    def upload(
+    def upsert(
         self,
         catalog: str,
         schema: str,
         table: str,
-        format: UploadFormat,
-        mode: UploadMode,
         content: bytes,
+        mode: Optional[UpsertMode] = None,
         primary_key: Optional[str] = None,
     ) -> None:
         params = {
             "catalog": catalog,
             "schema": schema,
             "table": table,
-            "format": format.value,
-            "mode": mode.value,
         }
+        if mode is not None:
+            params["mode"] = mode.value
         if primary_key:
             params["primary_key"] = primary_key
         try:
             res = self._client.post(
-                "/upload",
+                "/upsert",
                 params=params,
                 content=content,
-                headers={"Content-Type": "application/octet-stream"},
             )
             self._check_response(res)
         except httpx.RequestError as e:
diff --git a/src/altertable_lakehouse/models.py b/src/altertable_lakehouse/models.py
index d69725e..2c4c950 100644
--- a/src/altertable_lakehouse/models.py
+++ b/src/altertable_lakehouse/models.py
@@ -11,13 +11,7 @@ class ComputeSize(str, Enum):
     XL = "XL"
 
 
-class UploadFormat(str, Enum):
-    CSV = "csv"
-    JSON = "json"
-    PARQUET = "parquet"
-
-
-class UploadMode(str, Enum):
+class UpsertMode(str, Enum):
     CREATE = "create"
     APPEND = "append"
     UPSERT = "upsert"
diff --git a/tests/test_client.py b/tests/test_client.py
index f59c404..6c38d74 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -45,9 +45,9 @@ def test_query_all(client):
     assert isinstance(res.columns, list)
     assert isinstance(res.rows, list)
 
-def test_upload(client):
+def test_upsert(client):
     try:
-        client.upload(catalog="cat", schema="sch", table="tbl", format=models.UploadFormat.JSON, mode=models.UploadMode.APPEND, content=b'{"a":1}')
+        client.upsert(catalog="cat", schema="sch", table="tbl", mode=models.UpsertMode.APPEND, content=b'{"a":1}')
     except errors.BadRequestError:
         pass