From 103b3a9b816c817f70c73f757906c65c737ef9e0 Mon Sep 17 00:00:00 2001
From: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Date: Fri, 10 Jul 2026 07:06:52 +0000
Subject: [PATCH] fix(vertex-ai): default missing native content roles

---
 .../vertex_ai/google_genai/transformation.py  | 12 ++++++++--
 .../google_genai/test_transformation.py       | 24 +++++++++++++++++++
 2 files changed, 34 insertions(+), 2 deletions(-)
 create mode 100644 tests/test_litellm/llms/vertex_ai/google_genai/test_transformation.py

diff --git a/litellm/llms/vertex_ai/google_genai/transformation.py b/litellm/llms/vertex_ai/google_genai/transformation.py
index c1120d9ab8b..b8b056b4bb4 100644
--- a/litellm/llms/vertex_ai/google_genai/transformation.py
+++ b/litellm/llms/vertex_ai/google_genai/transformation.py
@@ -82,10 +82,18 @@ class VertexAIGoogleGenAIConfig(GoogleGenAIConfig):
         if generate_content_config_dict:
             self._normalize_response_schema(generate_content_config_dict, model)
 
-        # Build the request in Google GenAI format that Vertex AI expects
+        vertex_contents = (
+            [
+                {**content, "role": content.get("role", "user")} if isinstance(content, dict) else content
+                for content in contents
+            ]
+            if isinstance(contents, list)
+            else contents
+        )
+
         result = {
             "model": model,
-            "contents": contents,
+            "contents": vertex_contents,
         }
 
         # Add tools if provided
diff --git a/tests/test_litellm/llms/vertex_ai/google_genai/test_transformation.py b/tests/test_litellm/llms/vertex_ai/google_genai/test_transformation.py
new file mode 100644
index 00000000000..bfbabc43c19
--- /dev/null
+++ b/tests/test_litellm/llms/vertex_ai/google_genai/test_transformation.py
@@ -0,0 +1,24 @@
+from litellm.llms.vertex_ai.google_genai.transformation import (
+    VertexAIGoogleGenAIConfig,
+)
+
+
+def test_transform_generate_content_request_defaults_omitted_role():
+    config = VertexAIGoogleGenAIConfig()
+    contents = [
+        {"parts": [{"text": "Hello"}]},
+        {"role": "model", "parts": [{"text": "Hi"}]},
+    ]
+
+    result = config.transform_generate_content_request(
+        model="gemini-2.5-flash",
+        contents=contents,
+        tools=None,
+        generate_content_config_dict={},
+    )
+
+    assert result["contents"] == [
+        {"role": "user", "parts": [{"text": "Hello"}]},
+        {"role": "model", "parts": [{"text": "Hi"}]},
+    ]
+    assert "role" not in contents[0]