> ## Documentation Index
> Fetch the complete documentation index at: https://docs.crun.ai/llms.txt
> Use this file to discover all available pages before exploring further.
# Flux 2 Flex
> Flux 2 Flex from Black Forest Labs gives you control over the quality-speed trade-off when generating images. Unlike typical text-to-image models that make these decisions for you, Flex lets you adjust how many steps to run and how strongly the model should follow your prompt.
## Query Task Status
After submitting a task, use the unified query endpoint to check progress and retrieve results:
Learn how to query task status and retrieve generation results
For production use, we recommend using the `callback_url` parameter to receive automatic notifications when generation completes, rather than polling the status endpoint.
## Related Resources
Explore all available models
Check credits and account usage
## OpenAPI
````yaml models/flux/flux-2-flex.json post /api/v1/client/job/CreateTask
openapi: 3.0.0
info:
title: Crun Flux 2 Flex API
description: crun.ai Flux 2 Flex API Documentation
version: 1.0.0
contact:
name: Technical Support
email: support@crun.ai
servers:
- url: https://api.crun.ai
description: API Server
security:
- ApiKeyAuth: []
paths:
/api/v1/client/job/CreateTask:
post:
summary: flux 2 flex image generation or editing.
operationId: flux-2-flex
requestBody:
required: true
content:
application/json:
schema:
type: object
required:
- model
- input
properties:
model:
type: string
enum:
- flux-2-flex
description: |-
The model name to use for generation. Required field.
- Must be `flux-2-flex` for this endpoint
callback_url:
type: string
format: uri
description: >-
Optional. Callback URL for receiving task completion
notifications.
- System will POST task status and results to this URL when
generation completes
- Callback payloads structure is consistent with the `data`
object returned by the task status query
- Your callback endpoint should accept POST requests with
JSON payload containing results
- It returns an HTTP 200 status code upon successful receipt
example: https://your-domain.com/api/callback
input:
type: object
description: >-
Input parameters for the Flux 2 Flex model, offering
granular control over inference steps, guidance, and
multi-image referencing.
properties:
prompt:
type: string
description: Text prompt for image generation.
minLength: 1
maxLength: 5000
example: >-
A surreal painting of a clock melting over a futuristic
city skyline, vibrant sunset colors.
img_urls:
type: array
description: >-
List of input image URLs for image-to-image generation.
Supports up to 10 images (overriding the standard 8).
items:
type: string
format: uri
maxItems: 10
example:
- https://example.com/ref-1.jpg
- https://example.com/ref-2.jpg
prompt_upsampling:
type: boolean
description: >-
If true, the model will automatically refine and expand
your prompt for more creative results.
default: false
example: true
steps:
type: integer
description: >-
Number of inference steps. Higher values can improve
detail but take longer.
minimum: 1
maximum: 50
default: 30
example: 40
guidance:
type: number
description: >-
Guidance scale. Controls how strictly the model follows
the prompt vs. its own creativity.
minimum: 1.5
maximum: 10
default: 4.5
example: 7.5
aspect_ratio:
type: string
description: Aspect ratio of the generated image.
enum:
- '1:1'
- '2:3'
- '3:2'
- '3:4'
- '4:3'
- '4:5'
- '5:4'
- '9:16'
- '16:9'
- match_input_image
default: match_input_image
example: '16:9'
resolution:
type: string
description: >-
Resolution in megapixels. Up to 4 MP is possible, but 2
MP or below is recommended. The maximum image size is
2048x2048, which means that high-resolution images may
not respect the resolution if aspect ratio is not 1:1.
enum:
- 1K
- 2K
- 4K
default: 1K
safety_tolerance:
type: integer
description: Safety filter sensitivity (1-5).
minimum: 1
maximum: 5
default: 2
seed:
type: integer
description: Random seed for generation.
output_format:
type: string
enum:
- png
- jpg
- webp
default: webp
output_quality:
type: integer
description: >-
Quality when saving the output images, from 0 to 100.
100 is best quality, 0 is lowest quality. Not relevant
for `png` outputs
minimum: 0
maximum: 100
default: 80
required:
- prompt
example:
model: replicate/flux-2-flex
callback_url: https://your-domain.com/api/callback
input:
prompt: >-
An ethereal forest with glowing flora, captured in a macro
photography style.
img_urls:
- https://example.com/macro_reference.png
prompt_upsampling: true
steps: 40
guidance: 6
aspect_ratio: '4:3'
resolution: 2K
output_format: png
responses:
'200':
description: Request successful
content:
application/json:
schema:
allOf:
- $ref: '#/components/schemas/ApiResponse'
- type: object
properties:
data:
type: object
properties:
task_id:
type: string
description: >-
Task ID, can be used with Get Task Details
endpoint to query task status
example: task_12345678
example:
code: 200
message: success
data:
task_id: task_12345678
'422':
description: Validation Error
content:
application/json:
schema:
allOf:
- $ref: '#/components/schemas/ApiResponse'
- type: object
properties:
errors:
type: array
description: Detailed validation error messages
items:
type: string
example:
- specific error field message
example:
code: 422
message: Missing Params or Type Error
errors:
- specific error field message
'500':
$ref: '#/components/responses/Error'
components:
schemas:
ApiResponse:
type: object
properties:
code:
type: integer
enum:
- 200
- 401
- 402
- 404
- 422
- 429
- 455
- 500
- 501
- 505
description: >-
Response status code
- **200**: Success - Request has been processed successfully
- **401**: Unauthorized - Authentication credentials are missing or
invalid
- **402**: Insufficient Credits - Account does not have enough
credits to perform the operation
- **404**: Not Found - The requested resource or endpoint does not
exist
- **422**: Validation Error - The request parameters failed
validation checks
- **429**: Rate Limited - Request limit has been exceeded for this
resource
- **455**: Service Unavailable - System is currently undergoing
maintenance
- **500**: Server Error - An unexpected error occurred while
processing the request
- **501**: Generation Failed - Content generation task failed
- **505**: Feature Disabled - The requested feature is currently
disabled
message:
type: string
description: Response message, error description when failed
example: success
responses:
Error:
description: Server Error
securitySchemes:
ApiKeyAuth:
type: apiKey
in: header
name: x-api-key
description: >-
All APIs require authentication via API Key.
Get API Key:
1. Visit [API Key Management Page](https://crun.ai/user-api-key) to get
your API Key
Usage:
Add to request header:
x-api-key: YOUR_API_KEY
Note:
- Keep your API Key secure and do not share it with others
- If you suspect your API Key has been compromised, reset it immediately
in the management page
````