curl -X GET "https://router.example.com/v1/router/cost?from=2024-06-01T00:00:00Z&to=2024-06-30T23:59:59Z&group_by=user,model" \
  -H "Authorization: Bearer <api-key>"

{
  "items": [
    {
      "user": "user_a",
      "model": "gpt-4o",
      "cost_usd": 12.45,
      "tokens": 41500
    },
    {
      "user": "user_a",
      "model": "claude-3-5-sonnet-20241022",
      "cost_usd": 8.20,
      "tokens": 27300
    }
  ]
}