diff --git a/litellm/llms/custom_httpx/llm_http_handler.py b/litellm/llms/custom_httpx/llm_http_handler.py
index 0a5364bfcfec..518a28f11458 100644
--- a/litellm/llms/custom_httpx/llm_http_handler.py
+++ b/litellm/llms/custom_httpx/llm_http_handler.py
@@ -3015,7 +3015,8 @@ def create_file(
 
         # Store the upload URL in litellm_params for the transformation method
         litellm_params_with_url = dict(litellm_params)
-        litellm_params_with_url["upload_url"] = api_base
+        if "upload_url" not in litellm_params:
+            litellm_params_with_url["upload_url"] = api_base
 
         return provider_config.transform_create_file_response(
             model=None,
diff --git a/tests/test_litellm/llms/bedrock/files/test_bedrock_files_integration.py b/tests/test_litellm/llms/bedrock/files/test_bedrock_files_integration.py
index 37a0daa1d500..fb09e5b6194b 100644
--- a/tests/test_litellm/llms/bedrock/files/test_bedrock_files_integration.py
+++ b/tests/test_litellm/llms/bedrock/files/test_bedrock_files_integration.py
@@ -5,9 +5,11 @@
 import base64
 from unittest.mock import AsyncMock, MagicMock, patch
 
+import httpx
 import pytest
 
 import litellm
+from litellm.llms.custom_httpx.llm_http_handler import BaseLLMHTTPHandler
 from litellm.types.llms.openai import HttpxBinaryResponseContent
 from litellm.types.utils import SpecialEnums
 
@@ -108,3 +110,64 @@ async def test_litellm_afile_content_bedrock_provider_with_unified_file_id(self)
             assert call_kwargs["_is_async"] is True
             # The handler extracts S3 URI from the unified file ID
             assert call_kwargs["file_content_request"]["file_id"] == encoded_file_id
+
+    def test_sync_create_file_preserves_provider_upload_url(self):
+        """
+        Test that sync create_file does not overwrite upload_url set by the
+        provider's transform_create_file_request.
+
+        Regression test for https://github.com/BerriAI/litellm/issues/21546
+        where the sync path unconditionally overwrote litellm_params["upload_url"]
+        with api_base, causing the returned file_id to point to the wrong S3 key.
+        """
+        handler = BaseLLMHTTPHandler()
+
+        # The provider sets upload_url during transform_create_file_request
+        # (this is what Bedrock does at bedrock/files/transformation.py:370)
+        provider_upload_url = "https://s3.us-east-1.amazonaws.com/bucket/correct-uuid-key.jsonl"
+        # api_base holds a stale URL from the first get_complete_file_url call
+        stale_api_base = "https://s3.us-east-1.amazonaws.com/bucket/stale-uuid-key.jsonl"
+
+        litellm_params = {"upload_url": provider_upload_url}
+
+        mock_provider = MagicMock()
+        # transform_create_file_request returns a pre-signed dict (Bedrock path)
+        mock_provider.transform_create_file_request.return_value = {
+            "method": "PUT",
+            "url": provider_upload_url,
+            "headers": {"Authorization": "AWS4-HMAC-SHA256 ..."},
+            "data": b"file-content",
+        }
+        mock_provider.validate_environment.return_value = {}
+        mock_provider.get_complete_file_url.return_value = stale_api_base
+
+        mock_response = httpx.Response(
+            status_code=200,
+            headers={"ETag": '"abc123"', "Content-Length": "100"},
+            request=httpx.Request(method="PUT", url=provider_upload_url),
+        )
+        mock_provider.transform_create_file_response.return_value = MagicMock()
+
+        mock_client = MagicMock()
+        mock_client.put.return_value = mock_response
+
+        handler.create_file(
+            create_file_data={"file": b"data", "purpose": "batch"},
+            litellm_params=litellm_params,
+            provider_config=mock_provider,
+            api_base=stale_api_base,
+            api_key="fake-key",
+            headers={},
+            logging_obj=MagicMock(),
+            client=mock_client,
+            timeout=30,
+            _is_async=False,
+        )
+
+        # The key assertion: transform_create_file_response must receive
+        # the provider's upload_url, NOT the stale api_base
+        call_kwargs = mock_provider.transform_create_file_response.call_args.kwargs
+        assert call_kwargs["litellm_params"]["upload_url"] == provider_upload_url, (
+            "upload_url was overwritten with stale api_base; "
+            "provider's upload_url should be preserved"
+        )