BFL API Integration Guide

Use this skill when integrating BFL FLUX APIs into applications for image generation, editing, and processing.

First: Check API Key

Before generating images, verify your API key is set:

echo $BFL_API_KEY

If empty or you see "Not authenticated" errors, see API Key Setup below.

Important: Image URLs Expire in 10 Minutes

Result URLs from the API are temporary. Download images immediately after generation completes - do not store or cache the URLs themselves.

When to Use

Setting up BFL API client
Implementing async polling patterns
Handling rate limits and errors
Configuring webhooks for production
Selecting regional endpoints
Building production-ready integrations

Quick Reference

Base Endpoints

Region	Endpoint	Use Case
Global	`https://api.bfl.ai`	Default, automatic failover
EU	`https://api.eu.bfl.ai`	GDPR compliance
US	`https://api.us.bfl.ai`	US data residency

Model Endpoints & Pricing

Credit pricing: 1 credit = $0.01 USD. FLUX.2 uses megapixel-based pricing (cost scales with resolution).

FLUX.2 Models

Model	Path	1st MP	+MP	1MP T2I	1MP I2I	Best For
FLUX.2 [klein] 4B	`/v1/flux-2-klein-4b`	1.4c	0.1c	$0.014	$0.015	Real-time, high volume
FLUX.2 [klein] 9B	`/v1/flux-2-klein-9b`	1.5c	0.2c	$0.015	$0.017	Balanced quality/speed
FLUX.2 [pro]	`/v1/flux-2-pro`	3c	1.5c	$0.03	$0.045	Production, fast turnaround
FLUX.2 [max]	`/v1/flux-2-max`	7c	3c	$0.07	$0.10	Maximum quality
FLUX.2 [flex]	`/v1/flux-2-flex`	6c	6c	$0.06	$0.12	Typography, adjustable controls
FLUX.2 [dev]	-	-	-	Free	Free	Local development (non-commercial)

Pricing formula: (firstMP + (outputMP-1) * mpPrice) + (inputMP * mpPrice) in cents

FLUX.1 Models

Model	Path	Price/Image	Best For
FLUX.1 Kontext [pro]	`/v1/flux-kontext`	$0.04	Image editing with context
FLUX.1 Kontext [max]	`/v1/flux-kontext-max`	$0.08	Max quality editing
FLUX1.1 [pro]	`/v1/flux-pro-1.1`	$0.04	Standard T2I, fast & reliable
FLUX1.1 [pro] Ultra	`/v1/flux-pro-1.1-ultra`	$0.06	Ultra high-resolution
FLUX1.1 [pro] Raw	`/v1/flux-pro-1.1-raw`	$0.06	Candid photography feel
FLUX.1 Fill [pro]	`/v1/flux-pro-1.0-fill`	$0.05	Inpainting

Tip: All FLUX.2 models support image editing via the input_image parameter - no separate editing endpoint needed. Use bfl.ai/pricing calculator for exact costs at different resolutions.

Image Input for Editing

Preferred: Use URLs directly - simpler and more convenient than base64.

Single image editing:

curl -X POST "https://api.bfl.ai/v1/flux-2-pro" \
  -H "x-key: $BFL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "prompt": "Change the background to a sunset",
    "input_image": "https://example.com/photo.jpg"
  }'

Multi-reference editing:

curl -X POST "https://api.bfl.ai/v1/flux-2-pro" \
  -H "x-key: $BFL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "prompt": "The person from image 1 in the environment from image 2",
    "input_image": "https://example.com/person.jpg",
    "input_image_2": "https://example.com/background.jpg"
  }'

The API fetches URLs automatically. Both URL and base64 work, but URLs are recommended when available.

Multi-Reference I2I

FLUX.2 models support multiple input images for combining elements, style transfer, and character consistency:

Model	Max References
FLUX.2 [klein]	4 images
FLUX.2 [pro/max/flex]	8 images

Parameters: input_image, input_image_2, input_image_3, ... input_image_8

Prompt pattern: Reference images by number in your prompt:

"The subject from image 1 in the environment from image 2"
"Apply the style of image 2 to the scene in image 1"
"The person from image 1 wearing the outfit from image 2, in the pose from image 3"

For detailed multi-reference patterns (character consistency, style transfer, pose guidance), see flux-best-practices/rules/multi-reference-editing.md

Rate Limits

Tier	Concurrent Requests
Standard (most endpoints)	24

Polling vs Webhooks

Approach	Use When
Polling	Scripts, CLI tools, local development, single requests, simple integrations
Webhooks	Production apps, high volume, server-to-server, when you need immediate notification

Start with polling - it's simpler and works everywhere. Switch to webhooks when you need to scale or want event-driven architecture.

Key Behaviors

Polling: Response includes polling_url for async results
URL Expiration: Result URLs expire after 10 minutes
Webhook Support: Configure webhook_url for production workloads

API Key Setup

Required: The BFL_API_KEY environment variable must be set before using the API.

Quick Check

echo $BFL_API_KEY

If Not Set

Get a key: Go to https://dashboard.bfl.ai/get-started → Click "Create Key" → Select organization

Save to .env (recommended for persistence):

echo 'BFL_API_KEY=bfl_your_key_here' >> .env
echo '.env' >> .gitignore  # Don't commit secrets

See references/api-key-setup.md for detailed setup instructions.

Authentication

x-key: YOUR_API_KEY

Basic Request Flow

1. POST request to model endpoint
   └─> Response: { "polling_url": "..." }

2. GET polling_url (repeat until complete)
   └─> Response: { "status": "Pending" | "Ready" | "Error", ... }

3. When Ready, download result URL
   └─> URL expires in 10 minutes - download immediately

Prompting best practices (T2I, I2I, typography, colors): see the flux-best-practices skill
Multi-reference patterns (character consistency, style transfer, pose guidance): see flux-best-practices/rules/multi-reference-editing.md

References

references/api-key-setup.md - API key creation and configuration
references/endpoints.md - Complete endpoint documentation
references/polling-patterns.md - Async polling implementation
references/rate-limiting.md - Rate limit handling strategies
references/error-handling.md - Error codes and recovery
references/webhook-integration.md - Webhook setup and security

Code Examples

Note: cURL examples are preferred by default as they work universally without requiring Python or Node.js. Use language-specific clients when building production applications.

references/code-examples/curl-examples.sh - cURL examples (recommended)
references/code-examples/python-client.py - Python client
references/code-examples/typescript-client.ts - TypeScript client

Quick Start Example

1. Submit Generation Request

curl -s -X POST "https://api.bfl.ai/v1/flux-2-pro" \
  -H "x-key: $BFL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"prompt": "A serene mountain landscape at sunset", "width": 1024, "height": 1024}'

Response:

{ "id": "abc123", "polling_url": "https://api.bfl.ai/v1/get_result?id=abc123" }

2. Poll for Result

curl -s "POLLING_URL" -H "x-key: $BFL_API_KEY"

Response when ready:

{ "status": "Ready", "result": { "sample": "https://...", "seed": 1234 } }

3. Download Image

curl -s -o output.png "IMAGE_URL"

Tip: Result URLs expire in 10 minutes. Download immediately after status becomes Ready.

4. Multi-Reference Example

Combine elements from multiple images:

curl -s -X POST "https://api.bfl.ai/v1/flux-2-pro" \
  -H "x-key: $BFL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "prompt": "The cat from image 1 sitting in the cozy room from image 2",
    "input_image": "https://example.com/cat.jpg",
    "input_image_2": "https://example.com/room.jpg",
    "width": 1024,
    "height": 1024
  }'

Reference images by number in your prompt. See Multi-Reference I2I for limits and patterns.

bfl-api