> ## Documentation Index > Fetch the complete documentation index at: https://docs.goenhance.ai/llms.txt > Use this file to discover all available pages before exploring further. # Kling 4.0 Flash > Kling 4.0 Flash, the faster and lower-cost version of Kuaishou's Kling 4.0. Text-to-video, or image-to-video from a **first frame**. 720p only, single takes of up to **20 seconds**. **Audio** — every generated video comes with a native audio track. It is always on: the model has no switch for it, so `sound` / `generate_audio` are rejected. **Pricing** — per second of generated video, in tokens (USD at $0.02/token). Text-to-video and image-to-video cost the same: | resolution | tokens/s | USD/s | |---|---|---| | 720p | 5.5715 | $0.11143 | Example: a 5-second video costs 27.86 tokens. Returns an `img_uuid`; poll GET /api/v1/jobs/detail (or use `custom_callback_url`) to get the generated video. **Not accepted by this model** (rejected before any tokens are charged): `image_end_url` and `keyframes` (Flash takes a first frame only — use [Kling 4.0](/api-reference/video-generations/kling-4-0) for last and middle frames), reference images or videos (use [Kling 4.0 Flash Reference to Video](/api-reference/video-generations/kling-4-0-flash-refs)), `sound` / `generate_audio` (audio is always generated), `negative_prompt`, `seed`, `model_params.multi_shot`, and 1080p / 4K. ## OpenAPI ````yaml api-reference/video-generations/openapi-kling-4-0-flash.json POST /api/v1/videos/generations openapi: 3.1.0 info: title: GoEnhance API - Kling 4.0 Flash description: >- Video generation with Kling 4.0 Flash. Same endpoint as the other Kling models; the model is selected by model. version: 1.0.0 servers: - url: https://api.goenhance.ai security: [] paths: /api/v1/videos/generations: post: tags: - VideoGenerations summary: Kling 4.0 Flash description: >- Kling 4.0 Flash, the faster and lower-cost version of Kuaishou's Kling 4.0. Text-to-video, or image-to-video from a **first frame**. 720p only, single takes of up to **20 seconds**. **Audio** — every generated video comes with a native audio track. It is always on: the model has no switch for it, so `sound` / `generate_audio` are rejected. **Pricing** — per second of generated video, in tokens (USD at $0.02/token). Text-to-video and image-to-video cost the same: | resolution | tokens/s | USD/s | |---|---|---| | 720p | 5.5715 | $0.11143 | Example: a 5-second video costs 27.86 tokens. Returns an `img_uuid`; poll GET /api/v1/jobs/detail (or use `custom_callback_url`) to get the generated video. **Not accepted by this model** (rejected before any tokens are charged): `image_end_url` and `keyframes` (Flash takes a first frame only — use [Kling 4.0](/api-reference/video-generations/kling-4-0) for last and middle frames), reference images or videos (use [Kling 4.0 Flash Reference to Video](/api-reference/video-generations/kling-4-0-flash-refs)), `sound` / `generate_audio` (audio is always generated), `negative_prompt`, `seed`, `model_params.multi_shot`, and 1080p / 4K. parameters: - name: Authorization in: header description: '' required: false example: '{{Authorization}}' schema: type: string requestBody: content: application/json: schema: type: object description: >- Kling 4.0 Flash text-to-video and image-to-video (first frame only). **Pricing** — per second of generated video: - 720p — 5.5715 tokens ($0.11143) properties: model: type: string enum: - kling-4-0-flash description: Model name. Must be `kling-4-0-flash` on this page. prompt: type: string maxLength: 2500 description: >- Text prompt describing the scene, motion and camera. Required, up to 2500 characters. image_url: type: string format: uri description: >- First-frame image URL. If provided, runs image-to-video (the aspect ratio follows this image); otherwise text-to-video. Up to 10MB, width and height at least 300px, aspect ratio between 2:5 and 5:2. Smaller images are upscaled automatically. duration: type: integer minimum: 3 maximum: 20 default: 5 description: Video duration in seconds, any integer from 3 to 20. resolution: type: string enum: - 720p default: 720p description: >- Output resolution. Kling 4.0 Flash only supports 720p. `quality` is accepted as a compatible alias. ratio: type: string enum: - '16:9' - '9:16' - '1:1' - '21:9' default: '16:9' description: >- Aspect ratio. Text-to-video only; ignored when `image_url` is provided. custom_callback_url: type: string format: uri description: >- Optional. A publicly accessible HTTPS URL. When the task status changes (processing / success / failed), GoEnhance sends a POST request to this URL. The request body is identical to the response of GET /api/v1/jobs/detail. If your server does not respond with HTTP 200, the notification is retried up to 3 times, with a 3-second timeout per attempt. example: https://your-server.com/goenhance/callback required: - model - prompt example: model: kling-4-0-flash prompt: >- The product slowly rotates on a marble pedestal, soft studio light, the camera pushes in for a close-up of the logo image_url: https://your-cdn.com/product-front.jpg duration: 8 responses: '200': description: '' content: application/json: schema: type: object properties: code: type: integer msg: type: string data: type: object properties: img_uuid: type: string cost: type: number description: >- Tokens deducted for this request. This is the amount actually charged, so it already reflects any discount active on your account and can be lower than the listed price. Tokens are deducted when the task is accepted, and refunded automatically if the generation ends in failure. example: 5.82 required: - img_uuid - cost required: - code - msg - data examples: '1': summary: Success value: code: 0 msg: Success data: img_uuid: c12b656c-747a-44fd-9c80-add79b0c52d5 cost: 5.82 '2': summary: Insufficient tokens value: code: 100 msg: tokens is not enough quota: summary: API key quota exceeded value: code: 101 msg: 'API key quota exceeded: 4990 of 5000 tokens used (monthly)' headers: {} '401': description: '' content: application/json: schema: type: object properties: code: type: integer msg: type: string required: - code - msg examples: '1': summary: Unauthorized value: code: 401 msg: Unauthorized headers: {} deprecated: false security: [] ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.