Feature Request

Motivation

When using forward_client_headers_to_llm_api with Anthropic OAuth (spend tokens), the cost of the LLM call is billed to the client's Anthropic account, not to the API key configured on the LiteLLM proxy. However, there is currently no way to distinguish these requests in the spend logs or database — they look identical to requests where LiteLLM's own API key was charged.

This makes it impossible to reconcile costs: without this signal, operators can't tell which spend log entries represent real costs against their LiteLLM API key vs. costs that were allocated to an end-user's Anthropic account.

Current Behavior

• forward_client_headers_to_llm_api forwards x-* and anthropic-beta headers to the LLM provider, but no record of this is stored in spend logs.
• StandardLoggingMetadata has requester_custom_headers (enterprise, populated for observability integrations), but SpendLogsMetadata does not — so this data never reaches the DB.
• The Authorization header (which carries the OAuth Bearer token) is not in the forwarded set anyway, so even requester_custom_headers wouldn't capture it.

Desired Behavior

Spend logs should include enough information to determine that a request used client-forwarded auth headers, so operators can identify requests where costs were billed to the client's account rather than the proxy's API key. For example:

• A flag or field in SpendLogsMetadata indicating that forward_client_headers_to_llm_api was active for the request
• Or propagating requester_custom_headers into SpendLogsMetadata so it reaches the DB

Use Case

Operator runs LiteLLM proxy with forward_client_headers_to_llm_api enabled for certain model groups. Some users authenticate with their own Anthropic OAuth tokens (spend tokens). The operator needs to filter spend logs to separate:

1. Requests billed to the proxy's Anthropic API key (real cost to operator)
2. Requests billed to the end-user's Anthropic account via forwarded auth (no cost to operator)