Determinism and Reproducibility

Use seed when a request needs repeatable behavior for tests, evals, or debugging. LatentKit forwards the seed only to providers that support a seed-like parameter and reports the result in determinism.

{
  "messages": [{ "role": "user", "content": "Return one JSON action." }],
  "seed": 42
}

Successful responses include:

{
  "determinism": {
    "seed_requested": 42,
    "seed_honored": true,
    "provider_supports_seed": true
  }
}

If a routed provider does not support seeds, LatentKit drops the parameter before the upstream call and returns:

{
  "determinism": {
    "seed_requested": 42,
    "seed_honored": false,
    "provider_supports_seed": false,
    "dropped_reason": "provider_does_not_support_seed"
  }
}

Provider support

Prefer deterministic routing

For evals and test harnesses, send one of these headers with a seeded request:

prefer_deterministic: true

X-LK-Prefer-Deterministic: true

When this hint is present, LatentKit keeps the published policy strategy but ranks seed-supporting routes ahead of non-seed routes inside that strategy.

Reproducibility limits

Even with seed, two different providers will produce different outputs. Pin the model with your routing policy when exact reproducibility matters. Also log response.provider, response.model, response.id, and response.policy_version_id so you can tell whether a replay used the same route.