diff --git a/llama_stack/apis/agents/agents.py b/llama_stack/apis/agents/agents.py
index c19f28054..9b77ab8c7 100644
--- a/llama_stack/apis/agents/agents.py
+++ b/llama_stack/apis/agents/agents.py
@@ -155,9 +155,7 @@ class AgentConfigCommon(BaseModel):
     toolgroups: Optional[List[AgentToolGroup]] = Field(default_factory=list)
     client_tools: Optional[List[ToolDef]] = Field(default_factory=list)
     tool_choice: Optional[ToolChoice] = Field(default=ToolChoice.auto)
-    tool_prompt_format: Optional[ToolPromptFormat] = Field(
-        default=ToolPromptFormat.json
-    )
+    tool_prompt_format: Optional[ToolPromptFormat] = Field(default=None)
 
     max_infer_iters: int = 10
 
diff --git a/tests/client-sdk/agents/test_agents.py b/tests/client-sdk/agents/test_agents.py
index c6be91232..4a8fdd36a 100644
--- a/tests/client-sdk/agents/test_agents.py
+++ b/tests/client-sdk/agents/test_agents.py
@@ -98,7 +98,6 @@ def agent_config(llama_stack_client, text_model_id):
         },
         toolgroups=[],
         tool_choice="auto",
-        tool_prompt_format="json",
         input_shields=available_shields,
         output_shields=available_shields,
         enable_session_persistence=False,