Google

Imagen 4

imagen-4.0-fast

Google's text-to-image series, focused on in-image text rendering and complex lighting, offering Fast, Standard, and Ultra tiers that trade off quality against cost

imagen-4.0 imagen-4.0-fast imagen-4.0-ultra

Try imagen-4.0-fast

Input

Showcases

View all showcases

Output

image

Fill in the parameters and run — results show up here.

Pricing

imagen-4.0-fast per image

Unit Price	$0.030

Positioning Overview

Imagen 4.0 fast is the fast text-to-image model in the same family, aimed at developers who need low-cost, low-latency batch image generation. It accepts text prompts and outputs images, supporting negative prompts, random seeds, and multiple aspect ratios, making it easy to embed the generation process into product prototypes, batch content production, and creative drafting. Compared with the standard and Ultra versions in the same family, it is better suited to scenarios that are sensitive to generation speed and per-image cost, and where the precision requirements for the final image can be relaxed.

Key Highlights

The fast generation tier in the same family — trades lighter-weight generation for shorter waits, suitable for workflows that first produce drafts and then decide whether to refine them.
Supports seeds and negative prompts — a fixed seed reproduces the same result, and negative prompts exclude unwanted content, making regression testing and parameter tuning easier.
Aspect ratios cover common layouts — options include 1:1, 16:9, 9:16, 3:4, 4:3, and auto, directly matching the needs of social media, landscape, and portrait assets.
Prompt limit of 5000 characters — a single prompt can hold longer scene, composition, and style descriptions, reducing the communication cost of splitting multiple generations.

Capability Description

Text-prompt-to-image generation: pass in a descriptive prompt to get an image; the output is an image asset that can be directly integrated into content production and asset management workflows.

Negative prompt constraints: use negative_prompt to exclude unwanted elements or styles, reducing repeated retries and improving the usability rate of batch generation.

Random seed reproduction: specifying a seed stably reproduces the generation result for the same prompt, facilitating version comparison, A/B testing, and troubleshooting.

Flexible aspect ratios: aspect_ratio supports square, landscape, portrait, and auto, generating the appropriate layout for the delivery channel in one pass and reducing post-cropping.

Applicable Scenarios

Batch generation of social media images for content operations — batch-submit prompts and corresponding ratios by topic to produce landscape or portrait images ready for scheduled publishing.
Rapid creative drafting for product teams — generate multiple visual concepts at low cost during the proposal discussion stage, then decide on refinement directions after review and selection.
Layout placeholders in design workflows — generate placeholder images matching the target ratio for posters and landing pages, used for layout and information hierarchy validation.
Automated regression testing of generation pipelines — use fixed seeds and negative prompts to construct stable inputs and verify the stability and consistency of the image generation pipeline.

Limitations and Selection Advice

It accepts only text input and does not support image input or editing based on existing images; the prompt length limit is 5000 characters. As a fast tier, its output is better suited to drafts, placeholders, and batch assets. If there are higher requirements for detail sharpness, prompt adherence, or text accuracy within the image, the standard or Ultra version in the same family should be used instead; even when text within the image is generated successfully, manual verification is recommended. This model is not suitable when image editing or reference-image capabilities are needed.

What's new

View changelog →

Feature change Imagen 4 model IDs are now imagen-4.0… Oct 21, 2026
New model Added Google Imagen 4 image-generation docs Oct 14, 2026

Frequently asked questions

View all FAQs →

What is Imagen 4 good for?

Everyday product, lifestyle and content images. Describe the subject, scene, material and light to get an image ready for review, for product heroes, campaign drafts and editorial illustrations.
Which aspect ratios does Imagen 4 support?

Six: 1:1, 16:9, 9:16, 3:4, 4:3 and auto. aspect_ratio is required; the Playground on this page defaults to 16:9.
How long can the prompt be?

Up to 5,000 characters. prompt is required; order it as subject, scene, material, light and text.
Can I exclude things I don't want?

Yes, with negative_prompt. It is optional, up to 5,000 characters, and works for extra text, watermarks or a cluttered background.

Create a generation task

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

Headers

AuthorizationstringRequired

Account API key. Required on every request. Example: Bearer YOUR_HIAPI_API_KEY. Get your API key

Content-TypestringOptional

The request body is always parsed as JSON; when sent, only application/json (optionally with charset) is accepted — any other value returns 415. Example: application/json.

Idempotency-KeystringOptional

Idempotency key, up to 255 bytes. Retries with the same key from the same account create the task only once; replays return the original taskId.

Idempotency key

On network timeouts or client retries, the same key creates the task only once — no double charges (scope: the API key's account). Use a business-unique identifier as the key (e.g. "order-42"); replays return the original taskId, and keys expire 24 hours after the first request. See the Unified Async API overview for the full scenario matrix.

Body

modelstringRequired

Current fixed value: imagen-4.0-fast

routestringOptional

Current fixed value: default

inputobjectRequired

Business parameters for imagen-4.0-fast and route default — see the parameter table below.

seedintegerOptional

Optional, random seed used to reproduce the generated result; takes an integer.

promptstringRequiredminLength 1maxLength 5000

Prompt describing the image content to generate; takes a string.

aspect_ratiostringRequired

The aspect ratio of the output image, controlling the width-to-height ratio of the generated image; takes a string.

Options:1:116:99:163:44:3auto

negative_promptstringOptionalmaxLength 5000

Optional, negative prompt used to describe content to avoid; takes a string.

callbackobjectOptional

Terminal-state notification config. When omitted, no callback is delivered — poll the task yourself. See the callback note below.

Callbacks (Webhook)

Provide callback.url when creating a task and HiAPI POSTs to your service once the task reaches a terminal state — no polling needed. The callback payload mirrors the task detail structure; signature verification, delivery retries and idempotency are documented on the Unified Async API overview page.

urlstringRequired

Required when callback is present. A POST is sent to this URL once the task reaches a terminal state; must be a valid http(s) URL.

whenstringOptionalDefault: "final"

Only final is supported today — notified on both success and fail.

Options:final

storagestringOptionalDefault: "temp"

Artifact storage tier: temp (default, retained about 7 days) or persistent (long-term, billed by size). Insufficient balance or exceeding the storage cap silently downgrades to temp; the effective tier is shown in the task detail response.

Options:temppersistent

Request examples

# Submit an async task; returns a taskId immediately (no waiting for generation)
curl -X POST "https://api.hiapi.ai/v1/tasks" \
  -H "Authorization: Bearer $HIAPI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "model": "imagen-4.0-fast",
  "input": {
    "prompt": "…",
    "aspect_ratio": "…"
  }
}'

const res = await fetch("https://api.hiapi.ai/v1/tasks", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${process.env.HIAPI_API_KEY}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    model: "imagen-4.0-fast",
    input: {
      "prompt": "…",
      "aspect_ratio": "…"
    }
  }),
});
const task = await res.json();
// { code: 200, message: "success", data: { taskId } }

import os, requests

res = requests.post(
    "https://api.hiapi.ai/v1/tasks",
    headers={"Authorization": f"Bearer {os.environ['HIAPI_API_KEY']}"},
    json={
        "model": "imagen-4.0-fast",
        "input": {
          "prompt": "…",
          "aspect_ratio": "…"
        }
    },
)
print(res.json())  # { code, message, data: { taskId } }

200 OK

{
  "code": 200,
  "message": "success",
  "data": {
    "taskId": "tk-hiapi-01HZTQ8BX2N3GM3YFK4Z9D7VQR"
  }
}

400 Bad Request

{
  "code": 400,
  "message": "invalid request",
  "data": null,
  "error_code": "INVALID_REQUEST"
}

Get task detail

GET https://api.hiapi.ai/v1/tasks/:id

Response fields

taskIdstringRequired

Task ID, always prefixed with tk-hiapi-.

modelstringRequired

Resolved full model name. Tasks submitted with the route parameter return base@route (e.g. gpt-image-2/text-to-image@ext); otherwise identical to the name passed at creation.

routestringOptional

Present only when the task was submitted with an explicit route parameter; echoes the submitted value.

statusstringRequired

Task status.

Status values

queued Queued, not started yet. handling Being processed. archiving Processing finished, artifacts being prepared. success Terminal: completed, artifacts available (output returned). fail Terminal: failed (error returned). After submission, check status: success and fail are terminal, everything else is non-terminal. Poll every 1–3 seconds until terminal. On success, download artifacts from output[].url and transfer them before expireAt; pass storage: "persistent" at creation time when long-term retention is needed.

creatednumberRequired

Task creation time (Unix seconds).

completednumberRequired

Unix seconds when the task reached a terminal state; fixed to 0 while not terminal.

outputarrayOptional

Present only when status == success. Artifact list — always an array; a single task may return multiple types at once (e.g. video + first_frame).

Array [ object ]

Array items

urlstringRequired

Artifact URL, directly downloadable.

typestringRequired

Current possible values: video, image, audio, first_frame, last_frame, thumbnail; more may be added later.

expireAtnumberRequired

Unix seconds until which the artifact remains accessible; download or transfer before it expires.

errorobjectOptional

Present only when status == fail.

codestringRequired

Business error code.

messagestringRequired

Error description.

Response examples

Success

{
  "code": 200,
  "message": "success",
  "data": {
    "taskId": "tk-hiapi-01HZTQ8BX2N3GM3YFK4Z9D7VQR",
    "model": "happyhorse-1-0",
    "status": "success",
    "created": 1777282033,
    "completed": 1777282099,
    "output": [
      {
        "url": "https://cdn.hiapi.ai/tasks/.../video.mp4",
        "type": "video",
        "expireAt": 1777886899
      }
    ]
  }
}

Processing (non-terminal)

{
  "code": 200,
  "message": "success",
  "data": {
    "taskId": "tk-hiapi-...",
    "model": "happyhorse-1-0",
    "status": "archiving",
    "created": 1777282033,
    "completed": 0
  }
}

Failed

{
  "code": 200,
  "message": "success",
  "data": {
    "taskId": "tk-hiapi-...",
    "model": "happyhorse-1-0",
    "status": "fail",
    "created": 1777282033,
    "completed": 1777282099,
    "error": {
      "code": "TASK_FAILED",
      "message": "task failed"
    }
  }
}