Higgsfield API vs Runway API

Higgsfield API

One asynchronous API for 67 video and 17 image catalogue entries, with idempotency keys, per-second list prices public without a login, and failed or moderated jobs not charged. API inputs and outputs train Higgsfield's models unless the workspace opts out, and the docs carry no changelog. The API returns 400 at the concurrency limit, with no Retry-After.

Runway API

OpenAPI 3.1, llms.txt and Markdown copies of every docs page. Gen-3 Alpha Turbo and Gen-4 Aleph were removed on 2026-07-30 with no prior notice in the changelog.

Higgsfield API

1. Send Authorization: Key <key_id>:<key_secret> to https://api.higgsfield.ai. A Bearer token is rejected
2. Send a fresh Idempotency-Key with every generation. After a timeout or 5xx, repeat the same request with the same key, then read status_url
3. Treat a 400 whose detail mentions concurrent requests as a limit, not a bad request. Wait for a running job to finish before submitting more
4. Poll status_url from 2 seconds up to 10 with jitter, and stop on completed, failed, nsfw or canceled
5. Download output within seven days. Media files may be deleted after that
6. Read the model's own docs page for its schema. The OpenAPI file lists only a few models

Runway API

1. Send X-Runway-Version: 2024-11-06 on every request or it fails
2. Use the SDK's wait-for-output helper or poll GET /v1/tasks/{id} until SUCCEEDED or FAILED
3. Don't retry a SAFETY.* failure unchanged. It's moderation, not an outage
4. Take model IDs from the models page, not memory. Two were removed without notice on 2026-07-30
5. Copy outputs to your own storage. URLs expire within 24 to 48 hours