diff --git a/src/strands/models/sagemaker.py b/src/strands/models/sagemaker.py
index d1447732e..25b3ca7ce 100644
--- a/src/strands/models/sagemaker.py
+++ b/src/strands/models/sagemaker.py
@@ -4,7 +4,7 @@
 import logging
 import os
 from dataclasses import dataclass
-from typing import Any, AsyncGenerator, Literal, Optional, Type, TypedDict, TypeVar, Union, cast
+from typing import Any, AsyncGenerator, Literal, Optional, Type, TypedDict, TypeVar, Union
 
 import boto3
 from botocore.config import Config as BotocoreConfig
@@ -151,8 +151,8 @@ def __init__(
         validate_config_keys(payload_config, self.SageMakerAIPayloadSchema)
         payload_config.setdefault("stream", True)
         payload_config.setdefault("tool_results_as_user_messages", False)
-        self.endpoint_config = dict(endpoint_config)
-        self.payload_config = dict(payload_config)
+        self.endpoint_config = self.SageMakerAIEndpointConfig(**endpoint_config)
+        self.payload_config = self.SageMakerAIPayloadSchema(**payload_config)
         logger.debug(
             "endpoint_config=<%s> payload_config=<%s> | initializing", self.endpoint_config, self.payload_config
         )
@@ -193,7 +193,7 @@ def get_config(self) -> "SageMakerAIModel.SageMakerAIEndpointConfig":  # type: i
         Returns:
             The Amazon SageMaker model configuration.
         """
-        return cast(SageMakerAIModel.SageMakerAIEndpointConfig, self.endpoint_config)
+        return self.endpoint_config
 
     @override
     def format_request(
@@ -238,6 +238,10 @@ def format_request(
             },
         }
 
+        payload_additional_args = self.payload_config.get("additional_args")
+        if payload_additional_args:
+            payload.update(payload_additional_args)
+
         # Remove tools and tool_choice if tools = []
         if not payload["tools"]:
             payload.pop("tools")
@@ -273,16 +277,20 @@ def format_request(
         }
 
         # Add optional SageMaker parameters if provided
-        if self.endpoint_config.get("inference_component_name"):
-            request["InferenceComponentName"] = self.endpoint_config["inference_component_name"]
-        if self.endpoint_config.get("target_model"):
-            request["TargetModel"] = self.endpoint_config["target_model"]
-        if self.endpoint_config.get("target_variant"):
-            request["TargetVariant"] = self.endpoint_config["target_variant"]
-
-        # Add additional args if provided
-        if self.endpoint_config.get("additional_args"):
-            request.update(self.endpoint_config["additional_args"].__dict__)
+        inf_component_name = self.endpoint_config.get("inference_component_name")
+        if inf_component_name:
+            request["InferenceComponentName"] = inf_component_name
+        target_model = self.endpoint_config.get("target_model")
+        if target_model:
+            request["TargetModel"] = target_model
+        target_variant = self.endpoint_config.get("target_variant")
+        if target_variant:
+            request["TargetVariant"] = target_variant
+
+        # Add additional request args if provided
+        additional_args = self.endpoint_config.get("additional_args")
+        if additional_args:
+            request.update(additional_args)
 
         return request
 
diff --git a/tests/strands/models/test_sagemaker.py b/tests/strands/models/test_sagemaker.py
index a5662ecdc..72ebf01c6 100644
--- a/tests/strands/models/test_sagemaker.py
+++ b/tests/strands/models/test_sagemaker.py
@@ -112,11 +112,13 @@ def test_init_with_all_params(self, boto_session):
             "endpoint_name": "test-endpoint",
             "inference_component_name": "test-component",
             "region_name": "us-west-2",
+            "additional_args": {"test_req_arg_name": "test_req_arg_value"},
         }
         payload_config = {
             "stream": False,
             "max_tokens": 1024,
             "temperature": 0.7,
+            "additional_args": {"test_payload_arg_name": "test_payload_arg_value"},
         }
         client_config = BotocoreConfig(user_agent_extra="test-agent")
 
@@ -129,9 +131,11 @@ def test_init_with_all_params(self, boto_session):
 
         assert model.endpoint_config["endpoint_name"] == "test-endpoint"
         assert model.endpoint_config["inference_component_name"] == "test-component"
+        assert model.endpoint_config["additional_args"]["test_req_arg_name"] == "test_req_arg_value"
         assert model.payload_config["stream"] is False
         assert model.payload_config["max_tokens"] == 1024
         assert model.payload_config["temperature"] == 0.7
+        assert model.payload_config["additional_args"]["test_payload_arg_name"] == "test_payload_arg_value"
 
         boto_session.client.assert_called_once_with(
             service_name="sagemaker-runtime",
@@ -239,6 +243,30 @@ def test_get_config(self, model, endpoint_config):
     #     assert "tools" in payload
     #     assert payload["tools"] == []
 
+    def test_format_request_with_additional_args(self, boto_session, endpoint_config, messages, payload_config):
+        """Test formatting a request's `additional_args` where provided"""
+        endpoint_config_ext = {
+            **endpoint_config,
+            "additional_args": {
+                "extra_request_key": "extra_request_value",
+            },
+        }
+        payload_config_ext = {
+            **payload_config,
+            "additional_args": {
+                "extra_payload_key": "extra_payload_value",
+            },
+        }
+        model = SageMakerAIModel(
+            boto_session=boto_session,
+            endpoint_config=endpoint_config_ext,
+            payload_config=payload_config_ext,
+        )
+        request = model.format_request(messages)
+        assert request.get("extra_request_key") == "extra_request_value"
+        payload = json.loads(request["Body"])
+        assert payload.get("extra_payload_key") == "extra_payload_value"
+
     @pytest.mark.asyncio
     async def test_stream_with_streaming_enabled(self, sagemaker_client, model, messages):
         """Test streaming response with streaming enabled."""