diff --git a/rag/llm/chat_model.py b/rag/llm/chat_model.py
index a9e3c1ab7..dc59e1fb8 100644
--- a/rag/llm/chat_model.py
+++ b/rag/llm/chat_model.py
@@ -1632,25 +1632,22 @@ class LiteLLMBase(ABC):
                 raise ValueError("Bedrock auth_mode must be provided in the key")
 
             bedrock_region = bedrock_key.get("bedrock_region")
-            bedrock_credentials = {"bedrock_region": bedrock_region}
 
             if mode == "access_key_secret":
-                bedrock_credentials["aws_access_key_id"] = bedrock_key.get("bedrock_ak")
-                bedrock_credentials["aws_secret_access_key"] = bedrock_key.get("bedrock_sk")
+                completion_args.update({"aws_region_name": bedrock_region})
+                completion_args.update({"aws_access_key_id": bedrock_key.get("bedrock_ak")})
+                completion_args.update({"aws_secret_access_key": bedrock_key.get("bedrock_sk")})
             elif mode == "iam_role":
                 aws_role_arn = bedrock_key.get("aws_role_arn")
                 sts_client = boto3.client("sts", region_name=bedrock_region)
                 resp = sts_client.assume_role(RoleArn=aws_role_arn, RoleSessionName="BedrockSession")
                 creds = resp["Credentials"]
-                bedrock_credentials["aws_access_key_id"] = creds["AccessKeyId"]
-                bedrock_credentials["aws_secret_access_key"] = creds["SecretAccessKey"]
-                bedrock_credentials["aws_session_token"] = creds["SessionToken"]
-
-            completion_args.update(
-                {
-                    "bedrock_credentials": bedrock_credentials,
-                }
-            )
+                completion_args.update({"aws_region_name": bedrock_region})
+                completion_args.update({"aws_access_key_id": creds["AccessKeyId"]})
+                completion_args.update({"aws_secret_access_key": creds["SecretAccessKey"]})
+                completion_args.update({"aws_session_token": creds["SessionToken"]})
+            else:  # assume_role - use default credential chain (IRSA, instance profile, etc.)
+                completion_args.update({"aws_region_name": bedrock_region})
 
         elif self.provider == SupportedLiteLLMProvider.OpenRouter:
             if self.provider_order: