diff --git a/google/genai/batches.py b/google/genai/batches.py
index 77e2b34bf..0dbd0b8ac 100644
--- a/google/genai/batches.py
+++ b/google/genai/batches.py
@@ -1052,6 +1052,9 @@ def _GenerateContentConfig_to_mldev(
         'model_armor_config parameter is not supported in Gemini API.'
     )
 
+  if getv(from_object, ['service_tier']) is not None:
+    setv(parent_object, ['serviceTier'], getv(from_object, ['service_tier']))
+
   return to_object
 
 
diff --git a/google/genai/models.py b/google/genai/models.py
index 6a5bd8d6f..325a47251 100644
--- a/google/genai/models.py
+++ b/google/genai/models.py
@@ -1316,6 +1316,9 @@ def _GenerateContentConfig_to_mldev(
         'model_armor_config parameter is not supported in Gemini API.'
     )
 
+  if getv(from_object, ['service_tier']) is not None:
+    setv(parent_object, ['serviceTier'], getv(from_object, ['service_tier']))
+
   return to_object
 
 
@@ -1502,6 +1505,9 @@ def _GenerateContentConfig_to_vertex(
         getv(from_object, ['model_armor_config']),
     )
 
+  if getv(from_object, ['service_tier']) is not None:
+    raise ValueError('service_tier parameter is not supported in Vertex AI.')
+
   return to_object
 
 
diff --git a/google/genai/tests/models/test_generate_content.py b/google/genai/tests/models/test_generate_content.py
index bf5c0ea70..e37b5f54b 100644
--- a/google/genai/tests/models/test_generate_content.py
+++ b/google/genai/tests/models/test_generate_content.py
@@ -142,9 +142,7 @@ class InstrumentEnum(Enum):
             model=GEMINI_FLASH_LATEST,
             contents=t.t_contents('high'),
             config={
-                'system_instruction': t.t_content(
-                    'I say high, you say low'
-                )
+                'system_instruction': t.t_content('I say high, you say low')
             },
         ),
     ),
@@ -237,13 +235,13 @@ class InstrumentEnum(Enum):
             config=types.GenerateContentConfig(
                 tools=[{'google_maps': {}}],
                 tool_config={
-                    "retrieval_config": {
-                        "lat_lng": {
-                            "latitude": 37.421993,
-                            "longitude": -122.079725,
+                    'retrieval_config': {
+                        'lat_lng': {
+                            'latitude': 37.421993,
+                            'longitude': -122.079725,
                         }
                     }
-                }
+                },
             ),
         ),
     ),
@@ -357,9 +355,7 @@ class InstrumentEnum(Enum):
         name='test_speech_with_config',
         parameters=types._GenerateContentParameters(
             model='gemini-2.5-flash-preview-tts',
-            contents=t.t_contents(
-                'Produce a speech response saying "Cheese"'
-            ),
+            contents=t.t_contents('Produce a speech response saying "Cheese"'),
             config=types.GenerateContentConfig(
                 response_modalities=['audio'],
                 speech_config=types.SpeechConfig(
@@ -536,8 +532,8 @@ class InstrumentEnum(Enum):
         parameters=types._GenerateContentParameters(
             model=GEMINI_FLASH_LATEST,
             contents=t.t_contents(
-                'Summarize the evidence that confirms widespread voter fraud was'
-                ' the reason the last national election results were'
+                'Summarize the evidence that confirms widespread voter fraud'
+                ' was the reason the last national election results were'
                 ' inaccurate.'
             ),
             config={
@@ -562,6 +558,17 @@ class InstrumentEnum(Enum):
         ),
         exception_if_mldev='not supported',
     ),
+    pytest_helper.TestTableItem(
+        name='test_service_tier',
+        parameters=types._GenerateContentParameters(
+            model=GEMINI_FLASH_LATEST,
+            contents=t.t_contents('What is your name?'),
+            config={
+                'service_tier': 'flex',
+            },
+        ),
+        exception_if_vertex='not supported',
+    ),
 ]
 
 pytestmark = pytest_helper.setup(
diff --git a/google/genai/types.py b/google/genai/types.py
index 0ef38eb62..d8971d1c9 100644
--- a/google/genai/types.py
+++ b/google/genai/types.py
@@ -831,6 +831,19 @@ class ResourceScope(_common.CaseInSensitiveEnum):
       "https://aiplatform.googleapis.com/publishers/google/models/gemini-3-pro-preview"""
 
 
+class ServiceTier(_common.CaseInSensitiveEnum):
+  """Pricing and performance service tier."""
+
+  SERVICE_TIER_UNSPECIFIED = 'SERVICE_TIER_UNSPECIFIED'
+  """Default service tier, which is standard."""
+  SERVICE_TIER_FLEX = 'SERVICE_TIER_FLEX'
+  """Flex service tier."""
+  SERVICE_TIER_STANDARD = 'SERVICE_TIER_STANDARD'
+  """Standard service tier."""
+  SERVICE_TIER_PRIORITY = 'SERVICE_TIER_PRIORITY'
+  """Priority service tier."""
+
+
 class JSONSchemaType(Enum):
   """The type of the data supported by JSON Schema.
 
@@ -5937,6 +5950,10 @@ class GenerateContentConfig(_common.BaseModel):
       service. If supplied, safety_settings must not be supplied.
       """,
   )
+  service_tier: Optional[ServiceTier] = Field(
+      default=None,
+      description="""The service tier to use for the request. For example, FLEX.""",
+  )
 
   @pydantic.field_validator('response_schema', mode='before')
   @classmethod
@@ -6151,6 +6168,9 @@ class GenerateContentConfigDict(TypedDict, total=False):
       service. If supplied, safety_settings must not be supplied.
       """
 
+  service_tier: Optional[ServiceTier]
+  """The service tier to use for the request. For example, FLEX."""
+
 
 GenerateContentConfigOrDict = Union[
     GenerateContentConfig, GenerateContentConfigDict