Image generation API: what changes when you move from a UI to code

Most people arrive here from a web UI where you type a prompt and wait. Four things change when the same models are behind an API.

1. You get a job, not an image

{ "job_id": "abc123", "state": "queued", "credits_held": 4 }

Observe an accepted job through polling or an authenticated SSE stream. Customer webhook URLs are not part of the create contract. A later failed job can be described in a successful status response, so inspect state as well as the HTTP status. Submission errors themselves can return non-2xx responses.

2. Billing is per call, not per month

Model	Credits per image	Batch	Resolution
Flux	5	up to 4	No top-level selector
Nano Banana	4	up to 4	No top-level selector
Ideogram	6	up to 4	No top-level selector

No subscription tier gates which model you can use. You hold a credit balance and each call draws down from it; failed jobs refund in full.

3. Request rate is per key; concurrency is per user

Tier	Requests per minute	Concurrent jobs
Free	5	1
Pro	60	5

One in-flight job on the free tier. Exceeding either returns a 429 — and the two 429s need opposite responses, so branch on error.code rather than the status. See api rate limit exceeded and CONCURRENCY_LIMIT_EXCEEDED.

4. Parameters are validated locally

A value outside a model’s schema fails before anything is submitted, with the offending field named in error.param. No credits are touched. Each model has a different schema — see AI image API for the per-model references.

The minimal working call

curl -X POST https://genace.ai/api/v1/images/generations \
  -H "Authorization: Bearer $GENACE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"prompt":"a red ceramic mug on a white table"}'

No model needed — it defaults to Nano Banana at 4 credits ($0.04 at the Enterprise rate).

Continue with api fundamentals

• AI image API: the three models, what they cost, and how to call one
• AI video API: three models, one endpoint, and the async part that matters
• AI video API duration limits: how long a clip each model will make
• Browse all api fundamentals guides

Models covered on this page

• FLUX Pro
• Nano Banana
• Ideogram v3