Imagen 4 Fast
Google's Imagen 4 Fast: the quick, low-cost Imagen 4 tier for text-to-image.
First request
from openai import OpenAI
client = OpenAI(
base_url="https://api.altrouter.ai/v1",
api_key="ar-...",
)
img = client.images.generate(
model="imagen-4-fast",
prompt="a red fox in the snow",
)
print(img.data[0].url)import OpenAI from "openai";
const client = new OpenAI({
baseURL: "https://api.altrouter.ai/v1",
apiKey: process.env.ALTROUTER_API_KEY, // ar-...
});
const img = await client.images.generate({
model: "imagen-4-fast",
prompt: "a red fox in the snow",
});
console.log(img.data[0].url);curl https://api.altrouter.ai/v1/images/generations \
-H "Authorization: Bearer ar-..." \
-H "Content-Type: application/json" \
-d '{
"model": "imagen-4-fast",
"prompt": "a red fox in the snow"
}'The interface is OpenAI-compatible: in existing code only the base_url, the key and the model id change — nothing else.
Imagen 4 Fast against its price neighbours
| Model | Price | Unit | Discount | |
|---|---|---|---|---|
| Recraft Crisp UpscaleRecraft | $0.0034 | image | −15% | Open |
| Recraft Remove BackgroundRecraft | $0.0085 | image | −15% | Open |
| Imagen 4 Fastthis pageGoogle | $0.023 | image | — | |
| Qwen Image 3.0Alibaba | $0.028 | image | −8% | Open |
| Nano Banana 2 LiteGoogle | $0.028 | image | −17% | Open |
Prices and parameters come from the same catalog as the price above; this is not a benchmark, it is comparable billing terms.
Limits
Pricing is flat — $0.023 per image, regardless of prompt length. Allowed aspect_ratio values: 1:1, 16:9, 9:16, 3:4, 4:3.
There is no subscription: every successful request is billed at the price above, and a failed one is not billed at all. There is no markup over the vendor's official price. No Google account of your own is needed, and no VPN: requests go to api.altrouter.ai and we make the upstream call.
Rate limiting is shared across models and counted per key: 600 requests per minute by default, and a 429 with retry-after: 60 above it. An individual key can get its own limit and a spending cap per day, week, month or lifetime in the dashboard.
When to pick Imagen 4 Fast, and when a neighbour
The cheaper neighbour is Recraft Remove Background: $0.0085 per image against $0.023 for Imagen 4 Fast. On the same volume the bill comes out 2.7× smaller. It is the sensible pick where the task is repetitive and high-volume — labelling, classification, short templated answers — the kind of work where quality is bounded by the prompt rather than the model.
The dearer neighbour is Qwen Image 3.0: $0.028 per image, or 1.2× the price. On catalog parameters it offers the same capabilities and the same order of context, so the premium is only justified if Imagen 4 Fast falls short on your own task.
Guessing is more expensive than checking: the table above is prices and parameters, not a benchmark, and it cannot tell you which model does better on your own prompt. Switching costs one line — the model id in the request changes, the base_url and the key stay — so running both on your own data takes minutes.
OpenAI-compatible image generation endpoint. The result is re-hosted on our CDN and returned as a URL.
/v1/images/generations