Name: Claude Fable 5 API: Knowledge Work and Coding LLM
Brand: magicapi
SKU: api-magicapi-advanced-knowledge-work-coding-anthropic-claude-fable-5
Availability: InStock
Author: API Market

Shashank Agarwal

# 💡 Knowledge Work and Coding LLM API (Anthropic Claude Fable 5)

## Overview
Claude Fable 5 is a large language model from Anthropic. Its developer describes it as the next generation of intelligence for the hardest knowledge work and coding problems.

Send a text `prompt`, an optional `system_prompt` and an optional `image`. The model returns its answer as a list of text chunks; join them to get the full response. `max_tokens` allows answers of up to 128,000 tokens (minimum 1,024, default 8,192).

## Features
- **Text and image input**: ask about one optional `image` together with the `prompt`.
- **System prompt**: set the assistant's role, tone or rules with `system_prompt`.
- **Long answers**: `max_tokens` from 1,024 to 128,000 (default 8,192).
- **Image cost control**: `max_image_resolution` (0.001 to 2 megapixels, default 0.5) scales the image down before it is sent to the model, which lowers its input token count.
- **Token pricing**: you pay for the input and output tokens each request uses.

## Use Cases
1. **Coding help**: write, review and explain code, or plan multi-step changes.
2. **Research and analysis**: read, compare and summarize material and explain it from several angles.
3. **Image analysis**: describe screenshots, diagrams, charts or photos and answer questions about them.
4. **Long-form writing**: reports, briefs and structured explanations.

## Visual Examples
### Example Input
A photo of a room with "BUIO" and "WORK" wall art and the prompt "explain this through multiple philosophical lenses". `system_prompt` was empty and `max_tokens` and `max_image_resolution` were at their defaults (8,192 and 0.5).

![Input image: a room with a black poster reading BUIO with white flowers, a wall sign reading WORK in warped letters, a curved armchair and a green checkerboard floor](https://blog.api.market/wp-content/uploads/2026/10/claude-fable-5-input-api-market.jpg)

```json
{
  "image": "https://blog.api.market/wp-content/uploads/2026/10/claude-fable-5-input-api-market.jpg",
  "prompt": "explain this through multiple philosophical lenses",
  "max_tokens": 8192,
  "system_prompt": "",
  "max_image_resolution": 0.5
}
```

### Example Output
The model read the room through seven philosophical lenses (existentialism, Marxist critique, phenomenology, Daoism, Stoicism, postmodernism and absurdism) and closed with a synthesis, in Markdown (1,250 output tokens). An excerpt of the joined output:

```markdown
# A Philosophical Reading of This Room

## Existentialism
The pairing of **"BUIO"** (Italian for *darkness*) with **"WORK"** stages a classic existential tension. Darkness represents the void - the absence of inherent meaning - while "WORK," rendered in warped, almost melting letters, suggests the human project of *creating* meaning through labor and action. [...]

[...]

## Absurdism (Camus)
Darkness on one wall, toil on the other - Sisyphus's whole situation, framed and matted. Yet the room responds not with despair but with a pink lamp, soft seating, and flowers. One must imagine the inhabitant happy.
```

## Input Parameters
| Field | Type | Required | Default | Allowed values | Description |
| --- | --- | --- | --- | --- | --- |
| `prompt` | string | Yes |  |  | Input prompt |
| `image` | string (URL) | No | none |  | Optional input image. Images are priced as (width px * height px)/750 input tokens |
| `system_prompt` | string | No | `""` |  | System prompt |
| `max_tokens` | integer | No | `8192` | 1024 to 128000 | Maximum number of output tokens |
| `max_image_resolution` | number | No | `0.5` | 0.001 to 2 | Maximum image resolution in megapixels. Scales down image before sending it to Claude, to save time and money. |

## Pricing
- **Pay As You Go (PAYG) pricing**: you only pay for what you use.
- **Price**: $0.0063 per API unit.
- **1 API unit = 100 weighted tokens**; an output token counts 1, an input token counts 0.2.
- That is **$12.60 per million input tokens** and **$63.00 per million output tokens**.
- Each request's weighted token total is rounded up to a whole unit.
- **Example cost**: the example request used 699 input tokens and 1,250 output tokens: 699 x 0.2 + 1,250 = 1,389.8 weighted tokens, rounded up to 14 units = **$0.0882**.
- An input image counts as input tokens: (width px x height px) / 750, after it is scaled down to `max_image_resolution`. At the default 0.5 megapixels that is about 667 input tokens.
- **Failed or cancelled predictions are not billed.**
- **GET requests to check prediction status** are free and don't count toward API unit usage.
- **No monthly subscription fee.**

## API Documentation

### Base URL
All API requests go to: `https://prod.api.market/api/v1/magicapi/advanced-knowledge-work-coding-anthropic-claude-fable-5`

### Authentication
Send your api.market API key in the `x-api-market-key` header:
```
x-api-market-key: YOUR_API_MARKET_KEY
```

### Asynchronous Processing
**IMPORTANT**: This API is asynchronous. The flow is:
1. Send a POST request to `/predictions`. A successful request returns **201 Created** with a prediction `id` and a `status` of `starting` or `processing`.
2. Poll GET `/predictions/{id}` with that ID.
3. Keep polling while `status` is `starting` or `processing`.
4. Stop when `status` is `succeeded` (read `output`), `failed` or `canceled` (read `error`).

A polling interval of 1 second and an overall timeout of 600 seconds (10 minutes) work well.

### Endpoints

#### Create a Prediction
```bash
curl -X POST "https://prod.api.market/api/v1/magicapi/advanced-knowledge-work-coding-anthropic-claude-fable-5/predictions" \
  -H "Content-Type: application/json" \
  -H "x-api-market-key: YOUR_API_MARKET_KEY" \
  -d '{
    "version": "anthropic/claude-fable-5",
    "input": {
      "image": "https://blog.api.market/wp-content/uploads/2026/10/claude-fable-5-input-api-market.jpg",
      "prompt": "explain this through multiple philosophical lenses",
      "max_tokens": 8192,
      "system_prompt": "",
      "max_image_resolution": 0.5
    }
  }'
```

Response (201 Created):
```json
{
  "id": "exw0mvh7dhrmw0d1d0sb8tt388",
  "version": "anthropic/claude-fable-5",
  "status": "starting",
  "created_at": "2026-10-23T09:57:59.992Z"
}
```

#### Check Prediction Status
```bash
curl -X GET "https://prod.api.market/api/v1/magicapi/advanced-knowledge-work-coding-anthropic-claude-fable-5/predictions/{id}" \
  -H "x-api-market-key: YOUR_API_MARKET_KEY"
```

Response when the prediction has finished (200 OK):
```json
{
  "id": "exw0mvh7dhrmw0d1d0sb8tt388",
  "status": "succeeded",
  "output": [
    "# A",
    " Philosophical Reading",
    " of This Room",
    "\n\n##",
    " Existentialism\nThe",
    " p",
    "airing of **",
    "\"",
    "BUIO\"** (",
    "Italian for *",
    "darkness*) with",
    " **\"WORK\"** st",
    "ages",
    " a classic existential t",
    "ension."
  ],
  "error": null,
  "created_at": "2026-10-23T09:57:59.992Z",
  "started_at": "2026-10-23T09:58:00.492Z",
  "completed_at": "2026-10-23T09:58:23.330Z"
}
```

`output` is a list of text chunks. Join them in order to get the full response. The example above is cut to its first 15 chunks; the full response had 298.

### Status Codes
- **201 Created**: prediction created (POST `/predictions`). This is the normal success response.
- **200 OK**: prediction details returned (GET `/predictions/{id}`).
- **400 Bad Request**: invalid input, for example a missing `prompt` or a `max_tokens` value below 1,024.
- **401 Unauthorized**: missing or invalid API key.
- **404 Not Found**: no prediction with that ID.
- **429 Too Many Requests**: rate limit exceeded.
- **500 Internal Server Error** or **503 Service Unavailable**: temporary server problem; retry later.

## Rate Limits
All plans allow 10 requests per second. Requests above that return `429 Too Many Requests`; back off before retrying and honour any `Retry-After` header. Polling a prediction with GET is free but still counts toward the per-second limit, so poll every 1 to 5 seconds rather than in a tight loop.

## Error Handling
- Check the HTTP status code of every request and read the response body for the error message.
- A prediction can also end with `status` set to `failed`; the `error` field then explains why. Failed predictions are not billed.
- Retry 429, 500 and 503 responses with exponential backoff. Fix the input before retrying a 400.

## Implementation Guide
### Example Code

#### JavaScript
```javascript
const apiKey = "YOUR_API_MARKET_KEY";
const baseUrl = "https://prod.api.market/api/v1/magicapi/advanced-knowledge-work-coding-anthropic-claude-fable-5";

async function createAndWaitForPrediction(input) {
  const response = await fetch(`${baseUrl}/predictions`, {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      "x-api-market-key": apiKey
    },
    body: JSON.stringify({ version: "anthropic/claude-fable-5", input })
  });

  if (response.status !== 201) {
    throw new Error(`API error: ${response.status} ${await response.text()}`);
  }

  const prediction = await response.json();
  return pollForResults(prediction.id);
}

const delay = (ms) => new Promise((resolve) => setTimeout(resolve, ms));

async function pollForResults(predictionId) {
  const maxTimeout = 600000;
  const pollInterval = 1000;
  const startTime = Date.now();

  while (Date.now() - startTime < maxTimeout) {
    const response = await fetch(`${baseUrl}/predictions/${predictionId}`, {
      headers: { "x-api-market-key": apiKey }
    });

    if (!response.ok) {
      throw new Error(`API error: ${response.status} ${await response.text()}`);
    }

    const prediction = await response.json();

    if (prediction.status === "succeeded") {
      return prediction.output;
    }

    if (prediction.status === "failed" || prediction.status === "canceled") {
      throw new Error(`Prediction ${prediction.status}: ${prediction.error || "Unknown error"}`);
    }

    await delay(pollInterval);
  }

  throw new Error("Prediction timed out after 10 minutes");
}

createAndWaitForPrediction({
  "image": "https://blog.api.market/wp-content/uploads/2026/10/claude-fable-5-input-api-market.jpg",
  "prompt": "explain this through multiple philosophical lenses",
  "max_tokens": 8192,
  "system_prompt": "",
  "max_image_resolution": 0.5
}).then((output) => console.log(output.join("")));
```

#### Python
```python
import time
import requests

API_KEY = "YOUR_API_MARKET_KEY"
BASE_URL = "https://prod.api.market/api/v1/magicapi/advanced-knowledge-work-coding-anthropic-claude-fable-5"


def create_and_wait_for_prediction(input_data):
    headers = {"Content-Type": "application/json", "x-api-market-key": API_KEY}
    response = requests.post(
        f"{BASE_URL}/predictions",
        headers=headers,
        json={"version": "anthropic/claude-fable-5", "input": input_data},
    )

    if response.status_code != 201:
        raise Exception(f"API error: {response.status_code} {response.text}")

    return poll_for_results(response.json()["id"])


def poll_for_results(prediction_id):
    max_timeout = 600
    poll_interval = 1
    headers = {"x-api-market-key": API_KEY}
    start_time = time.time()

    while time.time() - start_time < max_timeout:
        response = requests.get(f"{BASE_URL}/predictions/{prediction_id}", headers=headers)

        if response.status_code != 200:
            raise Exception(f"API error: {response.status_code} {response.text}")

        prediction = response.json()

        if prediction["status"] == "succeeded":
            return prediction["output"]

        if prediction["status"] in ("failed", "canceled"):
            raise Exception(f"Prediction {prediction['status']}: {prediction.get('error') or 'Unknown error'}")

        time.sleep(poll_interval)

    raise Exception("Prediction timed out after 10 minutes")


output = create_and_wait_for_prediction({
    "image": "https://blog.api.market/wp-content/uploads/2026/10/claude-fable-5-input-api-market.jpg",
    "prompt": "explain this through multiple philosophical lenses",
    "max_tokens": 8192,
    "system_prompt": "",
    "max_image_resolution": 0.5
})
print("".join(output))
```

## FAQ
- **How do I get the full answer text?**
  - Join the strings in `output` in order: `output.join("")` in JavaScript or `"".join(output)` in Python.
- **How much does an image add?**
  - Images are counted as input tokens: (width px x height px) / 750 after scaling to `max_image_resolution`. At the default 0.5 megapixels that is about 667 input tokens, about $0.0084 at the input token rate. Lower `max_image_resolution` to pay less.
- **Can I send more than one image?**
  - No. Each request takes one optional `image` URL.
- **Does the API keep conversation history?**
  - No. Each request is independent. To continue a conversation, include the earlier turns in `prompt`.
- **What did the example request cost?**
  - 14 API units, $0.0882.
- **Is the 201 response from POST an error?**
  - No. 201 Created means the prediction was accepted. Use the returned `id` to poll GET `/predictions/{id}` until `status` is `succeeded`, `failed` or `canceled`.

## Contact Us
If you have any questions, reach out to us through the chat on the bottom right of the page. You can also email our support team at hello@magicapi.com.


Use Anthropic's Claude Fable 5 for hard knowledge work, coding and image analysis with one API key. Pay per token, no subscription or monthly fee.