Claude Fable 5.1 API — pricing & specs

Claude Fable 5.1, made by Anthropic, accepts text and image input and returns text. On KeepRouter, Claude Fable 5.1 costs $20.00 per 1M input tokens and $50.00 per 1M output tokens, billed pay-as-you-go with no monthly fee. Call it through a compatible KeepRouter endpoint supported by its active route, with the model id claude-fable-5-1.

MakerAnthropic
ModalityText, vision
Context window1,000,000 tokens
Max output128,000 tokens
Knowledge cutoff2026-06
Released2026-09-01
Input price$20.00 per 1M tokens
Output price$50.00 per 1M tokens
Cached input$0.2500 per 1M tokens
CapabilitiesVision (image input), Chat completions, Streaming where supported, Tool calling where supported
EndpointPOST /v1/chat/completions or POST /v1/messages (compatible chat routes)
Model idclaude-fable-5-1

How pricing works for Claude Fable 5.1

Claude Fable 5.1 is billed per token — $20.00 per 1M input tokens and $50.00 per 1M output tokens, with cached input at $0.2500 per 1M tokens. The published price is pay-as-you-go, with no monthly fee; actual request cost depends on measured token usage.

Calling Claude Fable 5.1 on KeepRouter

Point a compatible client at the supported KeepRouter endpoint and set the model to claude-fable-5-1. KeepRouter preserves the client-facing request shape while handling upstream routing or translation. Use POST /v1/chat/completions or, on compatible chat routes, POST /v1/messages; streaming and tool support depend on the model's active route.

cURL

curl https://keeprouter.com/v1/chat/completions \
  -H "Authorization: Bearer $KEEPROUTER_KEY" -H "Content-Type: application/json" \
  -d '{"model":"claude-fable-5-1","messages":[{"role":"user","content":"Hello"}]}'

Python

import os
from openai import OpenAI
client = OpenAI(base_url="https://keeprouter.com/v1", api_key=os.environ["KEEPROUTER_KEY"])
r = client.chat.completions.create(model="claude-fable-5-1", messages=[{"role":"user","content":"Hello"}])

JavaScript

import OpenAI from "openai";
const client = new OpenAI({ baseURL: "https://keeprouter.com/v1", apiKey: process.env.KEEPROUTER_KEY });
const r = await client.chat.completions.create({ model: "claude-fable-5-1", messages: [{ role: "user", content: "Hello" }] });

Estimate API costs

At the current KeepRouter customer price, an example workload of 1,000 total input tokens, no cached input, and 500 output tokens per request costs approximately $0.0450 per request. At 100 requests per day, that is $135.00 over 30 days. This is a usage estimate, excluding processing fees, taxes, retries and application infrastructure. Actual usage, cache hits and supported generation durations need their own checks.

Adjust quantities in the API cost calculator.

How to evaluate Claude Fable 5.1

Claude Fable 5.1 is listed on KeepRouter as text, vision under the exact id claude-fable-5-1. Use /v1/chat/completions for the listed route; a maker's upstream features do not automatically apply to this gateway endpoint. The published context window is 1,000,000 tokens and the published output limit is 128,000 tokens. These are limits, not a recommended request size.

First workload: Start with a text question plus one representative image, then repeat the same question with text only. Compare answer quality, latency and billed input/output tokens.

Before production: For agent use, test tool calls and structured output on this exact model route before production; an OpenAI-compatible chat endpoint alone does not prove either feature.

Agent setup paths

OpenCode

OpenCode documents a custom OpenAI-compatible provider. Set baseURL to https://keeprouter.com/v1 and list claude-fable-5-1 as a model; validate tool behavior on the exact route. Official setup.

{
  "$schema": "https://opencode.ai/config.json",
  "provider": {
    "keeprouter": {
      "npm": "@ai-sdk/openai-compatible",
      "name": "KeepRouter",
      "options": {
        "baseURL": "https://keeprouter.com/v1",
        "apiKey": "{env:KEEPROUTER_API_KEY}"
      },
      "models": {
        "claude-fable-5-1": {
          "name": "Claude Fable 5.1"
        }
      }
    }
  }
}

Continue

Continue documents provider: openai with a custom apiBase. Set apiBase to https://keeprouter.com/v1 and model to claude-fable-5-1; validate the selected feature and endpoint. Official setup.

name: KeepRouter
version: 0.0.1
schema: v1
models:
  - name: Claude Fable 5.1
    provider: openai
    model: claude-fable-5-1
    apiBase: https://keeprouter.com/v1
    apiKey: <YOUR_KEEPROUTER_API_KEY>

These are documented configuration paths; model-specific tool, streaming and multimodal behavior still needs a real request test.

Public model usage evidence

No public, exact-variant usage figure has been verified for this KeepRouter model id. Missing data is not zero usage; family-level or maker-wide traffic is not presented as this model's traffic.

Published examples and cases

No exact-model customer case has been verified for this entry. The workload above is an evaluation recipe, not a claim of a public deployment.

Source and verification boundary

Official Claude Fable 5.1 documentation. KeepRouter's live catalog is authoritative for the customer price and enabled endpoint shown here; the maker remains authoritative for upstream model capabilities and limits.

Pricing and implementation guides

Guides

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