After imagen-4.0-generate-001: read n from endpoints, use webhook mode

Ask the model's endpoints route how many images one request may return, cap your n at that, and send the request with mode: "webhook" so the images arrive on job.completed. Google shut down imagen-4.0-generate-001 on August 17, 2026 and points to gemini-nano-banana-2.1, and nothing guarantees the replacement takes the same per-request count as your old code assumed.

Where the number lives

Sume's image docs show each endpoint record with supported_parameters. n appears there as a range with min and max; the docs' example uses 1 to 4 for one model, which is an example, not a promise for yours. Read it for the id you call.

The submit

mode: "webhook" with a webhook_url makes /v1/images answer 202 with the job envelope; the images come later as artifacts in the job.completed payload. The webhook_url must be public HTTPS; localhost and private addresses are rejected. The sample prints the status and the cap it used.

Webhook delivery makes up to 10 attempts at 30-second spacing and can repeat, so dedupe on job_id. Keep a poll of status_url as a fallback for a missed delivery.

const base = process.env.SUME_BASE ?? "https://api.sume.com";
const headers = { Authorization: `Bearer ${process.env.SUME_API_KEY}`, "Content-Type": "application/json" };
const model = "google/nano-banana-2.1";

const meta = await (await fetch(`${base}/v1/images/models/${model}/endpoints`, { headers })).json();
const nMax = meta.endpoints[0].supported_parameters.n?.max ?? 1; // read it; do not assume Imagen's old count

const res = await fetch(`${base}/v1/images`, {
  method: "POST",
  headers: { ...headers, "Idempotency-Key": "catalog-shoot-0042" },
  body: JSON.stringify({ model, prompt: "ceramic mug on oak table", n: Math.min(4, nMax), mode: "webhook", webhook_url: "https://hooks.example.com/sume" }),
});
console.log(res.status, nMax); // 202 with the job envelope; the images arrive via job.completed

What this skips

The sample does not verify a signature, because it only sends; your receiver must check x-sume-webhook-signature before it trusts the body. It also uses a placeholder hook host, so swap in your own. A big n at high quality can exceed the 30-second wait in sync mode, which is the reason to go async here rather than hold an HTTP request open.