litellm - 💡(How to fix) Fix [Bug]: `attributes.metadata.spend_logs_metadata` sent as Python string instead of JSON in OpenTelemetry spans [1 pull requests]

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What happened?

When using the custom spend log metadata feature, the spend_logs_metadata value shows up in OpenTelemetry span attributes as a Python string representation ({'key': 'value'}) instead of a proper JSON string ({"key": "value"}). This makes it impossible to parse downstream in tools like Jaeger, Honeycomb, or Grafana Tempo.

Steps to Reproduce

Configure LiteLLM proxy with OpenTelemetry enabled (e.g. OTEL_EXPORTER=console is enough to observe the output).

1. Set up a success_callback callback in your config.yaml:

litellm_settings:
  success_callback: ["otel"]

general_settings:
  master_key: "sk-1234"

1. Make a request to the proxy and pass spend_logs_metadata as a dict in the request metadata:

curl -X POST http://localhost:4000/chat/completions \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer sk-1234" \
  -d '{
    "model": "gpt-4o",
    "messages": [{"role": "user", "content": "Hello"}],
    "metadata": {
      "spend_logs_metadata": {
        "project": "my-project",
        "env": "production"
      }
    }
  }'

1. Inspect the OTEL span output. The attributes.metadata.spend_logs_metadata attribute will look like this:

attributes.metadata.spend_logs_metadata = "{'project': 'my-project', 'env': 'production'}"

Expected:

attributes.metadata.spend_logs_metadata = "{\"project\": \"my-project\", \"env\": \"production\"}"

The single-quoted Python representation is not valid JSON and cannot be parsed by any standard JSON parser.

Relevant log output

What part of LiteLLM is this about?

SDK (litellm Python package)

What LiteLLM version are you on ?

v1.83.10

Twitter / LinkedIn details

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