Imagen 4 Fast API

POST Base URL: https://api.hiapi.ai /v1/tasks

Image, video, and audio models are called through theUnified Async API POST /v1/tasks endpoint; only the input fields differ (see input parameters below).

Model summary

Model name	imagen4-fast
Type	Image generation (text-to-image)
Endpoint	POST /v1/tasks
Pricing	See HiAPI Pricing

Imagen 4 Fast text-to-image API for high-quality images from detailed prompts.

Production guidance

Pass callback.url at the top level in production to reduce polling.
Poll GET /v1/tasks/:id for local debugging.

Best suited for

Try many visual directions quickly

Batch out versions to compare composition, color and style in 6 aspect ratios.

promptaspect_ratio

Fix an integer seed for A/B tests

Fix the integer seed and change one thing in the prompt at a time.

seednegative_prompt

Request parameters

POST https://api.hiapi.ai/v1/tasks

# Create an async task — returns taskId immediately (generation runs async)
# Replace YOUR_API_KEY with your account API key
curl -X POST "https://api.hiapi.ai/v1/tasks" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "model": "imagen4-fast",
  "input": {
    "prompt": "Create a quick concept illustration for a citrus soda ad. Show one can surrounded by orange slices and a refreshing splash in saturated orange and blue. Keep a single product scene with the can large in the frame. Flat, bright illustration style. Do not add logos or text.",
    "aspect_ratio": "16:9"
  }
}'

import requests, json

# Business params — fields vary by model (see the model page)
payload = json.loads(r'''
{
  "model": "imagen4-fast",
  "input": {
    "prompt": "Create a quick concept illustration for a citrus soda ad. Show one can surrounded by orange slices and a refreshing splash in saturated orange and blue. Keep a single product scene with the can large in the frame. Flat, bright illustration style. Do not add logos or text.",
    "aspect_ratio": "16:9"
  }
}
''')

# Create an async task — returns taskId immediately (generation runs async)
resp = requests.post(
    "https://api.hiapi.ai/v1/tasks",
    headers={"Authorization": "Bearer YOUR_API_KEY", "Content-Type": "application/json"},
    json=payload,
)
print(resp.json())  # Returns { code, message, data: { taskId } }

// Create an async task — returns taskId immediately (generation runs async)
// Replace YOUR_API_KEY with your account API key
const resp = await fetch("https://api.hiapi.ai/v1/tasks", {
  method: "POST",
  headers: {
    "Authorization": "Bearer YOUR_API_KEY",
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
  "model": "imagen4-fast",
  "input": {
    "prompt": "Create a quick concept illustration for a citrus soda ad. Show one can surrounded by orange slices and a refreshing splash in saturated orange and blue. Keep a single product scene with the can large in the frame. Flat, bright illustration style. Do not add logos or text.",
    "aspect_ratio": "16:9"
  }
}),
});
console.log(await resp.json()); // Returns { code, message, data: { taskId } }

model string required

Fixed value imagen4-fast.

example imagen4-fast

input object required

Put model parameters inside input.

prompt string required

Required image description, up to 5,000 characters.

aspect_ratio enum required

Output aspect ratio.

default 16:9 enum: 1:116:99:163:44:3auto

negative_prompt string optional

Optional negative prompt, up to 5,000 characters.

seed integer optional

Optional integer for reproducible generation.

callback object optional

Optional terminal task callback.

url string required

HTTPS endpoint that receives terminal task notifications.

example https://your-domain.com/hiapi/callback

when enum optional

Callback timing; keep final.

default final enum: final

Example requests

Draft a concept ad direction fast

A four-part prompt: the task, what to show, what to keep, and texture and limits.

Request body

{
  "model": "imagen4-fast",
  "input": {
    "prompt": "Create a quick concept illustration for a citrus soda ad. Show one can surrounded by orange slices and a refreshing splash in saturated orange and blue. Keep a single product scene with the can large in the frame. Flat, bright illustration style. Do not add logos or text.",
    "aspect_ratio": "16:9"
  }
}

Generate an icon set in one go

The prompt as submitted for an example on the model page.

Request body

{
  "model": "imagen4-fast",
  "input": {
    "prompt": "Flat vector icon set of weather symbols on a pastel background",
    "aspect_ratio": "1:1"
  }
}

Getting the result

The response returns a taskId immediately.
Wait for callback.url or poll GET /v1/tasks/:id.
When status=success, download output[].url.

FAQ

Does it accept reference images?

No. Imagen 4 Fast generates from text only.

What type is seed?

An optional integer. Note that seed is a string on Imagen 4 and Ultra.

What next once a direction is chosen?

Just change model. Carry the prompt and ratio to Google-Imagen4 or imagen4-ultra; note that seed is a string on those two.

How do I retrieve the result?

Use the taskId. The response returns it right away; download output[].url after the task succeeds.

How can I confirm the cost?

The task record is final. Check the pricing page and Playground estimate before submitting. View pricing