FLUX 3 Klein Image Edit API

Black Forest Labsimage$0.011 / image

Submit a FLUX 3 Klein Image Edit run over HTTP, then poll it or take a webhook. Results are files on media.ezflows.io. Try it in the playground first.

Async: the POST answers at once with a request id. Poll it, or take the webhook.

Docs

Submit

Parameters at the top level of the JSON body. Answers 202 with a request id.

curlPOST /v1/models/flux-3-klein-image-edit

curl -X POST https://api.ezflows.io/v1/models/flux-3-klein-image-edit \
  -H "Authorization: Bearer $EZFLOWS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "images": [
      "https://media.ezflows.io/inputs/<account>/<upload-id>.png"
    ],
    "prompt": "Recolour only the motorcycle'\''s fuel tank from cherry red to brushed copper. Keep the chrome, the tyres, the pegboard of hand tools, the brick wall and the lighting exactly unchanged.",
    "resolution": "1k",
    "aspect_ratio": "auto",
    "output_format": "jpeg"
  }'

# 202 Accepted, at once — it never waits for the model:
# {"request_id": "req_8f2a41c9b70e4d15", "status": "queued",
#  "poll_url": "https://api.ezflows.io/v1/requests/req_8f2a41c9b70e4d15"}

Poll

Same bearer header, every few seconds, until the status is final.

curlGET /v1/requests/:id

REQUEST_ID=req_8f2a41c9b70e4d15   # from the POST

while :; do
  BODY=$(curl -s https://api.ezflows.io/v1/requests/$REQUEST_ID \
    -H "Authorization: Bearer $EZFLOWS_API_KEY")
  STATUS=$(echo "$BODY" | jq -r .data.status)
  case "$STATUS" in succeeded|failed|cancelled) break ;; esac
  sleep 3
done

echo "$BODY" | jq -r '.data.output.artifacts[].url'   # media.ezflows.io, kept 90 days

Response

Files are on media.ezflows.io, kept 90 days. A failed run says why and costs nothing.

json200 · succeeded

{
  "data": {
    "id": "req_8f2a41c9b70e4d15",
    "model_slug": "flux-3-klein-image-edit",
    "status": "succeeded",
    "http_status": 200,
    "cost": 0.01144,
    "auth_method": "api_key",
    "error": null,
    "submitted_at": "2026-09-12T18:07:21.114Z",
    "queue_started_at": "2026-09-12T18:07:21.402Z",
    "execution_started_at": "2026-09-12T18:07:22.010Z",
    "first_byte_at": "2026-09-12T18:07:52.871Z",
    "finished_at": "2026-09-12T18:07:55.203Z",
    "io_deleted_at": null,
    "canvas_id": null,
    "canvas_node_id": null,
    "client_attempt_id": null,
    "idempotency_key": null,
    "input": {
      "images": [
        "https://media.ezflows.io/inputs/<account>/<upload-id>.png"
      ],
      "prompt": "Recolour only the motorcycle's fuel tank from cherry red to brushed copper. Keep the chrome, the tyres, the pegboard of hand tools, the brick wall and the lighting exactly unchanged.",
      "resolution": "1k",
      "aspect_ratio": "auto",
      "output_format": "jpeg"
    },
    "output": {
      "artifacts": [
        {
          "index": 0,
          "kind": "image",
          "contentType": "image/jpeg",
          "url": "https://media.ezflows.io/outputs/<account>/req_8f2a41c9b70e4d15/0.jpg"
        }
      ]
    }
  }
}

Webhook

Skip polling: we POST the result to your endpoint, at least once.

Register: Create an endpoint under Webhooks in the dashboard; the signing secret is shown once.
Events: request.succeeded · request.failed · request.cancelled
Headers: ezflows-event-id (dedupe on it) · ezflows-timestamp (unix seconds) · ezflows-signature t=<ts>,v1=<hex HMAC-SHA256 of "<ts>.<raw body>">
Verify: Over the exact bytes received, in constant time; reject anything older than five minutes.
Respond: Any 2xx within 10 s. Redirects are not followed.
Retries: Five, with backoff: 30 s · 60 s · 2 min · 4 min · 8 min. Disabled after five consecutive dead deliveries.

jsonDelivery body

{
  "id": "82cf46a4-841e-41d6-b3c7-facc937d3252",
  "type": "request.succeeded",
  "created_at": "2026-09-12T18:07:55Z",
  "data": {
    "id": "req_8f2a41c9b70e4d15",
    "model_slug": "flux-3-klein-image-edit",
    "status": "succeeded",
    "cost": 0.01144,
    "output": {
      "artifacts": [
        {
          "url": "https://media.ezflows.io/…/0.jpg"
        }
      ]
    }
  }
}

curlverify.sh

# Create the endpoint under Webhooks in the dashboard; the signing secret is shown once.
# ezflows-signature: t=<ts>,v1=<hex HMAC-SHA256 of "<ts>.<raw body>">
# body.json = the exact bytes received. Reject anything older than five minutes.
EXPECTED=$({ printf '%s.' "$TS"; cat body.json; } \
  | openssl dgst -sha256 -hmac "$EZFLOWS_WEBHOOK_SECRET" -r | cut -d' ' -f1)

[ "$EXPECTED" = "$V1" ] && echo "valid" || echo "reject"

Parameters 8

Name	Type	Default	Allowed	Description
imagesrequired	string[]	—	up to 10 image urls	1 to 10 images to edit, restyle or combine. The first is the image being edited. Refer to them in the prompt as Image 1, Image 2 or <ref_image_1>, <ref_image_2>. URL or base64.
promptrequired	string	Recolour only the motorcycle's fuel tank from cherry red to brushed copper. Keep the chrome, the tyres, the pegboard of hand tools, the brick wall and the lighting exactly unchanged.	—	What to change and what must stay the same. Supports bounding boxes: tag elements with <id> and append a JSON array of {id, bbox:[top,left,bottom,right] on a 0-1000 grid, desc}.
resolution	enum	1k	768sq · 1k · 1.5k · 2k · 4k	Output size tier (equal pixel area; exact dimensions follow the aspect ratio). Price scales with the tier.
aspect_ratio	enum	auto	auto · 21:9 · 2:1 · 16:9 · 3:2 · 7:5 · 4:3 · 5:4 · 1:1 · 4:5 · 3:4 · 5:7 · 2:3 · 9:16 · 1:2 · 9:21	auto keeps the first reference image's aspect ratio.
output_format	enum	jpeg	jpeg · png	jpeg (smaller) or png (lossless).
seed	integer	—	0–4294967295	Fix the seed to reproduce a result; leave empty for a random one.
steps	integer	16	1–16	Denoising steps of the distilled model. 16 is full quality; fewer is faster and rougher. Same price either way.
safety_tolerance	integer	2	0–4	Input and output moderation level: 0 is strictest, 4 most permissive.

File inputs (images: up to 10 image urls) take URLs. Upload the raw file to POST /v1/uploads with its own Content-Type and pass the url it returns. Inputs are kept 90 days.

Submit

Poll

Response

Webhook

Parameters 8

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