# FLUX.3 Klein Base

IMAGEFeaturedbfl-flux-3-klein-base

**FLUX.3 Klein Base** is the CFG base image model from [Black Forest Labs](https://blackforestlabs.ai/). It generates detailed images from a text prompt at 1K, 2K, or 4K, with up to four outputs and optional prompt expansion. Output aspect ratios include 16:9, 4:3, 1:1, and their portraits. It is the full base checkpoint, for artists who want that control instead of the step-distilled Klein variant.

Best for

CFG base text-to-image at 1K, 2K, and 4K, Detailed captions with optional prompt expansion

POST

/v2/workspaces/{workspace\_id}/base-models/bfl-flux-3-klein-base/inferences

```bash
curl --request POST \
  --url https://api.app.layer.ai/api/v2/workspaces/:workspace_id/base-models/bfl-flux-3-klein-base/inferences \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "prompt": "a knight standing in a snowy forest",
  "aspect_ratio": "SQUARE_1K"
}'
```

```python
import requests


url = "https://api.app.layer.ai/api/v2/workspaces/:workspace_id/base-models/bfl-flux-3-klein-base/inferences"


payload = {
    "prompt": "a knight standing in a snowy forest",
    "aspect_ratio": "SQUARE_1K"
}
headers = {
    "Authorization": "Bearer <token>",
    "Content-Type": "application/json"
}


response = requests.post(url, json=payload, headers=headers)


print(response.json())
```

```js
const url = 'https://api.app.layer.ai/api/v2/workspaces/:workspace_id/base-models/bfl-flux-3-klein-base/inferences';
const options = {
  method: 'POST',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: '{"prompt":"a knight standing in a snowy forest","aspect_ratio":"SQUARE_1K"}'
};


try {
  const response = await fetch(url, options);
  const data = await response.json();
  console.log(data);
} catch (error) {
  console.error(error);
}
```

```go
package main


import (
  "fmt"
  "strings"
  "net/http"
  "io"
)


func main() {


  url := "https://api.app.layer.ai/api/v2/workspaces/:workspace_id/base-models/bfl-flux-3-klein-base/inferences"


  payload := strings.NewReader("{\n  \"prompt\": \"a knight standing in a snowy forest\",\n  \"aspect_ratio\": \"SQUARE_1K\"\n}")


  req, _ := http.NewRequest("POST", url, payload)


  req.Header.Add("Authorization", "Bearer <token>")
  req.Header.Add("Content-Type", "application/json")


  res, _ := http.DefaultClient.Do(req)


  defer res.Body.Close()
  body, _ := io.ReadAll(res.Body)


  fmt.Println(res)
  fmt.Println(string(body))


}
```

```php
<?php


$curl = curl_init();


curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.app.layer.ai/api/v2/workspaces/:workspace_id/base-models/bfl-flux-3-klein-base/inferences",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
  CURLOPT_POSTFIELDS => json_encode([
    'prompt' => 'a knight standing in a snowy forest',
    'aspect_ratio' => 'SQUARE_1K'
  ]),
  CURLOPT_HTTPHEADER => [
    "Authorization: Bearer <token>",
    "Content-Type: application/json"
  ],
]);


$response = curl_exec($curl);
$err = curl_error($curl);


curl_close($curl);


if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}
```

```java
OkHttpClient client = new OkHttpClient();


MediaType mediaType = MediaType.parse("application/json");
RequestBody body = RequestBody.create(mediaType, "{\n  \"prompt\": \"a knight standing in a snowy forest\",\n  \"aspect_ratio\": \"SQUARE_1K\"\n}");
Request request = new Request.Builder()
  .url("https://api.app.layer.ai/api/v2/workspaces/:workspace_id/base-models/bfl-flux-3-klein-base/inferences")
  .post(body)
  .addHeader("Authorization", "Bearer <token>")
  .addHeader("Content-Type", "application/json")
  .build();


Response response = client.newCall(request).execute();
```

```ruby
require 'uri'
require 'net/http'


url = URI("https://api.app.layer.ai/api/v2/workspaces/:workspace_id/base-models/bfl-flux-3-klein-base/inferences")


http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true


request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Bearer <token>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"prompt\": \"a knight standing in a snowy forest\",\n  \"aspect_ratio\": \"SQUARE_1K\"\n}"


response = http.request(request)
puts response.read_body
```

```csharp
var client = new RestClient("https://api.app.layer.ai/api/v2/workspaces/:workspace_id/base-models/bfl-flux-3-klein-base/inferences");
var request = new RestRequest("", Method.Post);
request.AddHeader("Authorization", "Bearer <token>");
request.AddHeader("Content-Type", "application/json");
request.AddParameter("application/json", "{\n  \"prompt\": \"a knight standing in a snowy forest\",\n  \"aspect_ratio\": \"SQUARE_1K\"\n}", ParameterType.RequestBody);
var response = client.Execute(request);
```

* Layer API

## Authorizations

* **[bearerAuth](/docs/v2/rest-api#bearerauth)**
* **[oauth2](/docs/v2/rest-api#oauth2)**

## Parameters

### Path Parameters

**workspace\_id**

required

_Workspace Id_

Id of the workspace that owns the resource.

string format: uuid

Id of the workspace that owns the resource.

### Query Parameters

**session\_name**

_Session Name_

Organize this run under a named session. A new session is created if none matches.

string

nullable

Organize this run under a named session. A new session is created if none matches.

### Header Parameters

**Idempotency-Key**

string

<= 255 characters

Opaque key making a retry of this request return the first result. A 2xx response is replayed for 24 hours with `Idempotent-Replayed: true`. A 4xx releases the key. A 5xx, or a request still running, holds the key for 120 seconds, during which a retry gets 409; after that a retry executes again. The key covers the method, path, query, and byte-identical body it was first used with; reusing it for a different request is rejected with 422\. Protection is best effort: if the key store is unavailable, or a record is lost early, a retry can execute again even after an earlier 409\. See the Idempotency section of the API description.

## Request Bodyrequired

_FLUX.3 Klein Base_object

**prompt**

required

_Prompt_

Describe what to generate, or the change to make.

string

**aspect\_ratio**

_Aspect ratio_

The shape and size of the output.

string

default: SQUARE\_1K

Allowed values: SQUARE\_1K PORTRAIT\_3\_4\_1K PORTRAIT\_9\_16\_1K LANDSCAPE\_4\_3\_1K LANDSCAPE\_16\_9\_1K SQUARE\_2K PORTRAIT\_3\_4\_2K PORTRAIT\_9\_16\_2K LANDSCAPE\_4\_3\_2K LANDSCAPE\_16\_9\_2K SQUARE\_4K PORTRAIT\_3\_4\_4K PORTRAIT\_9\_16\_4K LANDSCAPE\_4\_3\_4K LANDSCAPE\_16\_9\_4K

**prompt\_enhancement**

_Prompt enhancement_

Let the model rewrite the prompt before generating.

_Advanced field._

string

default: AUTO

Allowed values: AUTO OFF STANDARD

**seed**

_Seed_

The starting point for the model’s randomness. The same seed and settings give the same result.

_Advanced field._

integer

nullable

**output\_fit**

_Output canvas_

Trim the transparent margin, and place the image on a canvas of a fixed size.

object

**trim**

_Trim_

boolean

**canvas**

_OutputFitCanvas_

string

default: CONTENT

Allowed values: CONTENT FIXED

**width**

_Width_

integer

nullable \>= 1 <= 4096

**height**

_Height_

integer

nullable \>= 1 <= 4096

**scale**

_OutputFitScale_

How the drawing goes onto a fixed canvas. The names follow the workflow Resize node’s.

string

default: PLACE

Allowed values: PLACE SHRINK\_AND\_PAD FIT\_AND\_PAD FIT\_AND\_CROP STRETCH

**anchor**

_OutputFitAnchor_

The point of the drawing that lands on the same point of the canvas.

`BASE` is a game tile’s base: its anchor, the bottom centre of the cell it stands on, lands at the bottom centre of the canvas, so tiles of one grid stand on the same point whatever rises above them.

string

default: CENTER

Allowed values: TOP\_LEFT TOP\_CENTER TOP\_RIGHT CENTER\_LEFT CENTER CENTER\_RIGHT BOTTOM\_LEFT BOTTOM\_CENTER BOTTOM\_RIGHT BASE

**padding**

_Padding_

integer

0 <= 512

**prompt\_language**

_Prompt language_

The language the prompt is written in, so it reaches the model as you meant it.

_Advanced field._

string

nullable

##### Example

```json
{
  "prompt": "a knight standing in a snowy forest",
  "aspect_ratio": "SQUARE_1K"
}
```

## Responses

### 202

Successful Response

_ExecuteForgeOutput_object

**inference\_id**

required

_Inference Id_

Unique identifier for this forge run.

string format: uuid

**status**

required

_InferenceStatus_

Current status: IN\_PROGRESS.

string

Allowed values: in\_progress complete failed cancelled deleted

**estimated\_price\_creative\_units**

_Estimated Price Creative Units_

Estimated price in Creative Units.

number

nullable

**poll\_interval\_seconds**

required

_Poll Interval Seconds_

Suggested polling interval in seconds.

integer

**created\_at**

required

_Created At_

Timestamp of when the run was created.

string format: date-time

**session\_id**

_Session Id_

Session ID the run was added to, if a session was specified.

string format: uuid

nullable

**normalized\_parameters**

Any of:

**NormalizedInferenceParameters**

_NormalizedInferenceParameters_

Inference parameters after model-specific normalization.

These reflect the actual values used for generation, including model defaults applied for any parameters not explicitly set.

object

**width**

_Width_

Resolved output width in pixels.

integer

nullable

**height**

_Height_

Resolved output height in pixels.

integer

nullable

**batch\_size**

_Batch Size_

Number of outputs to generate.

integer

nullable

**num\_inference\_steps**

_Num Inference Steps_

Resolved number of diffusion steps.

integer

nullable

**guidance\_scale**

_Guidance Scale_

Resolved guidance scale.

number

nullable

**duration\_seconds**

_Duration Seconds_

Resolved output length in seconds — video duration or audio clip length.

number

nullable

**fps**

_Fps_

Resolved FPS.

integer

nullable

**null**

null

##### Example

```json
{
  "status": "in_progress"
}
```

### 401

Unauthenticated — missing or invalid Bearer token.

object

**type**

required

string

**title**

required

string

**status**

required

integer

**detail**

required

string

##### Example

```json
{
  "type": "https://api.layer.ai/errors/ERROR_CODE",
  "title": "Error Title",
  "status": 400,
  "detail": "Human-readable description."
}
```

### 403

Forbidden — insufficient permissions, or the access token lacks the scope the operation requires.

object

**type**

required

string

**title**

required

string

**status**

required

integer

**detail**

required

string

##### Example

```json
{
  "type": "https://api.layer.ai/errors/ERROR_CODE",
  "title": "Error Title",
  "status": 400,
  "detail": "Human-readable description."
}
```

### 404

Resource not found.

object

**type**

required

string

**title**

required

string

**status**

required

integer

**detail**

required

string

##### Example

```json
{
  "type": "https://api.layer.ai/errors/ERROR_CODE",
  "title": "Error Title",
  "status": 400,
  "detail": "Human-readable description."
}
```

### 409

The outcome of the request with this `Idempotency-Key` is not known yet: it is still running, or it failed without a stored response. Retry after the number of seconds in `Retry-After`.

object

**type**

required

string

**title**

required

string

**status**

required

integer

**detail**

required

string

##### Example

```json
{
  "type": "https://api.layer.ai/errors/ERROR_CODE",
  "title": "Error Title",
  "status": 400,
  "detail": "Human-readable description."
}
```

### 422

Invalid input parameters, or an `Idempotency-Key` reused for a different request.

object

**type**

required

string

**title**

required

string

**status**

required

integer

**detail**

required

string

##### Example

```json
{
  "type": "https://api.layer.ai/errors/ERROR_CODE",
  "title": "Error Title",
  "status": 400,
  "detail": "Human-readable description."
}
```

### 429

Rate limited — retry after the number of seconds in `Retry-After`.

object

**type**

required

string

**title**

required

string

**status**

required

integer

**detail**

required

string

##### Example

```json
{
  "type": "https://api.layer.ai/errors/ERROR_CODE",
  "title": "Error Title",
  "status": 400,
  "detail": "Human-readable description."
}
```

### 500

Internal server error.

object

**type**

required

string

**title**

required

string

**status**

required

integer

**detail**

required

string

##### Example

```json
{
  "type": "https://api.layer.ai/errors/ERROR_CODE",
  "title": "Error Title",
  "status": 400,
  "detail": "Human-readable description."
}
```