if "form" in content_type:
    parsed_body = dict(await request.form())
    if "metadata" in parsed_body and isinstance(parsed_body["metadata"], str):
        parsed_body["metadata"] = json.loads(parsed_body["metadata"])

---

litellm_settings:
  drop_params: true

# intentionally empty — per-request user_config provides the model_list
model_list: []

---

litellm --config config.yaml --port 4000
# (or via Docker: ghcr.io/berriai/litellm:v1.81.0)

---

python -c "import base64,sys; sys.stdout.buffer.write(base64.b64decode('iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkAAIAAAoAAv/lxKUAAAAASUVORK5CYII='))" > tiny.png

---

curl -X POST http://localhost:4000/v1/images/edits \
  -H "Authorization: Bearer sk-1234" \
  -F "model=openai/gpt-image-1" \
  -F "prompt=test" \
  -F "[email protected]" \
  -F 'user_config={"model_list":[{"model_name":"openai/gpt-image-1","litellm_params":{"model":"openai/gpt-image-1","api_key":"sk-fake"}}]}'

---

curl -X POST http://localhost:4000/v1/images/generations \
  -H "Authorization: Bearer sk-1234" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-image-1",
    "prompt": "test",
    "user_config": {"model_list":[{"model_name":"openai/gpt-image-1","litellm_params":{"model":"openai/gpt-image-1","api_key":"sk-fake"}}]}
  }'

---

ERROR: common_request_processing.py:912 - litellm.proxy.proxy_server._handle_llm_api_exception():
Exception occured - litellm.router.Router() argument after ** must be a mapping, not str

Traceback (most recent call last):
  File "/usr/lib/python3.13/site-packages/litellm/proxy/image_endpoints/endpoints.py", line 288, in image_edit_api
    return await processor.base_process_llm_request(...)
  File "/usr/lib/python3.13/site-packages/litellm/proxy/common_request_processing.py", line 667, in base_process_llm_request
    llm_call = await route_request(...)
  File "/usr/lib/python3.13/site-packages/litellm/proxy/route_llm_request.py", line 200, in route_request
    user_router = litellm.Router(**router_config)
TypeError: litellm.router.Router() argument after ** must be a mapping, not str

The router_config at line 200 is the literal string '{"model_list":[...]}' — _read_request_body returned the form field as a string and route_request splatted it into Router().

Drop-in for the bug body

Use this as the "Actual behavior / log output" section:

**Actual response (500):**


{"error":{"message":"litellm.router.Router() argument after ** must be a mapping, not str","type":"None","param":"None","code":"500"}}


**Proxy traceback:**


TypeError: litellm.router.Router() argument after ** must be a mapping, not str

Traceback (most recent call last):
  File "litellm/proxy/image_endpoints/endpoints.py", line 288, in image_edit_api
    return await processor.base_process_llm_request(...)
  File "litellm/proxy/common_request_processing.py", line 667, in base_process_llm_request
    llm_call = await route_request(...)
  File "litellm/proxy/route_llm_request.py", line 200, in route_request
    user_router = litellm.Router(**router_config)


The crash happens because `_read_request_body`
(`litellm/proxy/common_utils/http_parsing_utils.py:40-43`) only JSON-decodes
the `metadata` field for multipart bodies. `user_config` arrives as a
JSON-shaped `str`, and `route_request` splats it directly into `Router()`.