diff --git a/src/strands/models/gemini.py b/src/strands/models/gemini.py
index c288595e1..154daff7c 100644
--- a/src/strands/models/gemini.py
+++ b/src/strands/models/gemini.py
@@ -214,7 +214,8 @@ def _format_request_config(
         """
         return genai.types.GenerateContentConfig(
             system_instruction=system_prompt,
-            tools=self._format_request_tools(tool_specs),
+            # NOTE: Vertex AI rejects empty arrays for `tools` due to oneof constraints
+            tools=self._format_request_tools(tool_specs) if tool_specs else None,
             **(params or {}),
         )
 
diff --git a/tests/strands/models/test_gemini.py b/tests/strands/models/test_gemini.py
index 9eb5a9a7f..dcaaa56b8 100644
--- a/tests/strands/models/test_gemini.py
+++ b/tests/strands/models/test_gemini.py
@@ -83,7 +83,7 @@ async def test_stream_request_default(gemini_client, model, messages, model_id):
     await anext(model.stream(messages))
 
     exp_request = {
-        "config": {"tools": [{"function_declarations": []}]},
+        "config": {},
         "contents": [{"parts": [{"text": "test"}], "role": "user"}],
         "model": model_id,
     }
@@ -97,10 +97,7 @@ async def test_stream_request_with_params(gemini_client, model, messages, model_
     await anext(model.stream(messages))
 
     exp_request = {
-        "config": {
-            "tools": [{"function_declarations": []}],
-            "temperature": 1,
-        },
+        "config": {"temperature": 1},
         "contents": [{"parts": [{"text": "test"}], "role": "user"}],
         "model": model_id,
     }
@@ -112,7 +109,7 @@ async def test_stream_request_with_system_prompt(gemini_client, model, messages,
     await anext(model.stream(messages, system_prompt=system_prompt))
 
     exp_request = {
-        "config": {"system_instruction": system_prompt, "tools": [{"function_declarations": []}]},
+        "config": {"system_instruction": system_prompt},
         "contents": [{"parts": [{"text": "test"}], "role": "user"}],
         "model": model_id,
     }
@@ -145,9 +142,7 @@ async def test_stream_request_with_document(content, formatted_part, gemini_clie
     await anext(model.stream(messages))
 
     exp_request = {
-        "config": {
-            "tools": [{"function_declarations": []}],
-        },
+        "config": {},
         "contents": [{"parts": [formatted_part], "role": "user"}],
         "model": model_id,
     }
@@ -172,9 +167,7 @@ async def test_stream_request_with_image(gemini_client, model, model_id):
     await anext(model.stream(messages))
 
     exp_request = {
-        "config": {
-            "tools": [{"function_declarations": []}],
-        },
+        "config": {},
         "contents": [
             {
                 "parts": [
@@ -213,9 +206,7 @@ async def test_stream_request_with_reasoning(gemini_client, model, model_id):
     await anext(model.stream(messages))
 
     exp_request = {
-        "config": {
-            "tools": [{"function_declarations": []}],
-        },
+        "config": {},
         "contents": [
             {
                 "parts": [
@@ -276,9 +267,7 @@ async def test_stream_request_with_tool_use(gemini_client, model, model_id):
     await anext(model.stream(messages))
 
     exp_request = {
-        "config": {
-            "tools": [{"function_declarations": []}],
-        },
+        "config": {},
         "contents": [
             {
                 "parts": [
@@ -326,9 +315,7 @@ async def test_stream_request_with_tool_results(gemini_client, model, model_id):
     await anext(model.stream(messages))
 
     exp_request = {
-        "config": {
-            "tools": [{"function_declarations": []}],
-        },
+        "config": {},
         "contents": [
             {
                 "parts": [
@@ -370,9 +357,7 @@ async def test_stream_request_with_empty_content(gemini_client, model, model_id)
     await anext(model.stream(messages))
 
     exp_request = {
-        "config": {
-            "tools": [{"function_declarations": []}],
-        },
+        "config": {},
         "contents": [{"parts": [], "role": "user"}],
         "model": model_id,
     }
@@ -613,7 +598,6 @@ async def test_structured_output(gemini_client, model, messages, model_id, weath
 
     exp_request = {
         "config": {
-            "tools": [{"function_declarations": []}],
             "response_mime_type": "application/json",
             "response_schema": weather_output.model_json_schema(),
         },