diff --git a/letta/llm_api/groq_client.py b/letta/llm_api/groq_client.py
index 5909f4d5..34edf622 100644
--- a/letta/llm_api/groq_client.py
+++ b/letta/llm_api/groq_client.py
@@ -34,6 +34,11 @@ class GroqClient(OpenAIClient):
     ) -> dict:
         data = super().build_request_data(agent_type, messages, llm_config, tools, force_tool_call, requires_subsequent_tool_call)
 
+        # Groq only supports string values for tool_choice: "none", "auto", "required"
+        # Convert object-format tool_choice (used for force_tool_call) to "required"
+        if "tool_choice" in data and isinstance(data["tool_choice"], dict):
+            data["tool_choice"] = "required"
+
         # Groq validation - these fields are not supported and will cause 400 errors
         # https://console.groq.com/docs/openai
         if "top_logprobs" in data:
diff --git a/letta/llm_api/openai_client.py b/letta/llm_api/openai_client.py
index eb61ed33..d7cce539 100644
--- a/letta/llm_api/openai_client.py
+++ b/letta/llm_api/openai_client.py
@@ -468,7 +468,12 @@ class OpenAIClient(LLMClientBase):
         tool_choice = None
         if tools:  # only set tool_choice if tools exist
             if force_tool_call is not None:
-                tool_choice = ToolFunctionChoice(type="function", function=ToolFunctionChoiceFunctionCall(name=force_tool_call))
+                # OpenRouter proxies to providers that may not support object-format tool_choice
+                # Use "required" instead which achieves similar effect
+                if is_openrouter:
+                    tool_choice = "required"
+                else:
+                    tool_choice = ToolFunctionChoice(type="function", function=ToolFunctionChoiceFunctionCall(name=force_tool_call))
             elif requires_subsequent_tool_call:
                 tool_choice = "required"
             elif self.requires_auto_tool_choice(llm_config) or agent_type == AgentType.letta_v1_agent: