curl --request POST \
  --url https://api.promptstream.ai/run_prompt \
  --header 'Content-Type: application/json' \
  --header 'X-API-Key: <x-api-key>' \
  --data '
{
  "prompt_id": "<string>",
  "inputs": {},
  "external_user_id": "<string>"
}
'

{
  "run_id": "<string>",
  "output": "<string>",
  "model_used": "<string>",
  "latency_ms": 123,
  "prompt_tokens": 123,
  "completion_tokens": 123,
  "total_tokens": 123,
  "token_cost_usd": 123,
  "variant_assigned": "<string>",
  "experiment_id": "<string>"
}