From Higgsfield API documentation: Lifecycle (R4) - every model uses the same authenticated asynchronous flow; a POST returns status "queued", a request_id, a status_url and a cancel_url; poll or receive a webhook; input media can be uploaded to Higgsfield storage first. Concurrency (R2) - the...

From Higgsfield API documentation: Lifecycle (R4) - every model uses the same authenticated asynchronous flow; a POST returns status "queued", a request_id, a status_url and a cancel_url; poll or receive a webhook; input media can be uploaded to Higgsfield storage first. Concurrency (R2) - the primary limit is the number of requests processing at once; above it, generation requests "are still accepted" and wait in the queue, while some non-generation endpoints (e.g. custom Soul ID reference training) return 429 with Retry-After; successful responses carry no remaining-capacity headers, so clients must track request_ids, cap submissions with a worker pool/semaphore, separate polling from submission, and back off with jitter. (Concurrency tiers by recent top-ups: 2/10/20/40 - C3-B516-01.) Billing (R1) - only successful generations are charged; requests ending "failed" or "nsfw" are refunded automatically if credits were reserved; a queued request can be cancelled (and refunded) only before processing starts; credits expire one year after being added; a POST /estimate/<model> with the same parameters returns credits and USD before submission. Retention (R1) - outputs are available for "at least seven days" and may then be removed, so download to your own storage. Auth (R3) - header "Authorization: Key KEY_ID:SECRET" (legacy hf-api-key/hf-secret headers still accepted); never call from browser/mobile code; separate dev/prod credentials; models unavailable to an account may return 404, 423 or 503. These confirm the creator's refund and one-year claims in C3-B516-01. Design implication for media pipelines: persist outputs immediately (seven-day window), treat moderation outcomes as non-billable terminal states in cost accounting, and pre-estimate costs for budget guards. Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Docs pages undated; MCP/CLI connector documentation not found in the API docs index. Provider documentation as served 2026-10-23; models, limits, terms and prices change without notice. Limitations: Docs pages undated; MCP/CLI connector documentation was not found in the API docs index; webhook signing and SDK details not read. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://docs.higgsfield.ai/docs/concepts/rate-limits.md",
      "note": "When concurrency is reached; Failed and moderated requests; Output retention"
    },
    {
      "url": "https://docs.higgsfield.ai/docs/concepts/billing-and-retention.md",
      "note": "When concurrency is reached; Failed and moderated requests; Output retention"
    }
  ]
}