curl -X GET https://app.tracia.io/api/v1/spans/sp_abc123def456 \
  -H "Authorization: Bearer tr_your_api_key"

{
  "id": "clx1abc123",
  "spanId": "sp_abc123def456",
  "traceId": "tr_session123",
  "parentSpanId": null,
  "promptSlug": "welcome-email",
  "promptVersion": 3,
  "model": "gpt-4o",
  "provider": "openai",
  "input": {
    "messages": [
      {
        "role": "system",
        "content": "You are a helpful assistant that writes professional emails."
      },
      {
        "role": "user",
        "content": "Write a welcome email for Alice who just signed up for Tracia."
      }
    ]
  },
  "variables": {
    "name": "Alice",
    "product": "Tracia"
  },
  "output": "Subject: Welcome to Tracia, Alice!\n\nDear Alice,\n\nThank you for signing up...",
  "status": "SUCCESS",
  "error": null,
  "latencyMs": 1250,
  "inputTokens": 150,
  "outputTokens": 320,
  "totalTokens": 470,
  "cost": 0.0234,
  "tags": ["production", "v2"],
  "userId": "user_123",
  "sessionId": "session_456",
  "createdAt": "2024-01-15T10:30:00.000Z"
}