claude-fable-5-1 — API, Pricing & Context Window | Vivgrid

claude-fable-5-1 is Anthropic's most capable model and sits above the Opus tier for the most demanding reasoning and long-horizon agentic work. It pairs a 1M-token context window with 128K-token max output and always-on adaptive thinking, so a single request can plan, execute, and verify work that would otherwise need several passes.

On Vivgrid, claude-fable-5-1 is geo-distributed across AMER, EMEA, and APAC and reachable on both the native Messages API (/messages) and Chat Completions (/chat/completions) with one unified key, so switching an agent from claude-opus-5 is a model-string change whichever surface you already use.

Specifications

Pricing

Pricing in USD per 1M tokens, matching the provider's rates.

What one request costs

The rates above applied to a 20K-token prompt with a 2K-token reply — a typical single agent turn, small enough that every request is billed at the base rate.

Prompt caching is billed at $12.50 per 1M cache-write tokens on the 5-minute TTL and $20.00 per 1M on the 1-hour TTL, with cached reads at $0.50 — half the cache-read rate of claude-fable-5.

Use claude-fable-5-1 in your coding agent

claude-fable-5-1 works with the same Vivgrid key and https://api.vivgrid.com/v1 endpoint as every other model in the catalog. Grab your API key from the Vivgrid Console, then drop one of the configurations below into your agent of choice.

Claude Code

Install Claude Code:

npm install -g @anthropic-ai/claude-code

claude-fable-5-1 is served on Vivgrid's native Messages API (/messages), so Claude Code connects directly. Point it at Vivgrid and select the model in ~/.claude/settings.json:

{
  "env": {
    "ANTHROPIC_AUTH_TOKEN": "viv-xxxxxxxxxxxxx",
    "ANTHROPIC_BASE_URL": "https://api.vivgrid.com/",
    "ANTHROPIC_MODEL": "claude-fable-5-1"
  }
}

Then start Claude Code in your project:

claude

Want different Vivgrid models for the Opus, Sonnet and Haiku slots? See the full Claude Code tutorial.

OpenCode

OpenCode has Vivgrid built in, so you can use claude-fable-5-1 without writing any config: open /models, search for vivgrid, paste your API key and pick the model. The OpenCode tutorial walks through it step by step.

Prefer to configure it by hand? Install OpenCode:

npm i -g opencode-ai

Declare claude-fable-5-1 under the Vivgrid provider in your global OpenCode config, ~/.config/opencode/opencode.json. The @ai-sdk/anthropic provider talks to Vivgrid over the Messages API (/v1/messages):

{
  "$schema": "https://opencode.ai/config.json",
  "model": "vivgrid/claude-fable-5-1",
  "provider": {
    "vivgrid": {
      "npm": "@ai-sdk/anthropic",
      "name": "Vivgrid",
      "options": {
        "baseURL": "https://api.vivgrid.com/v1",
        "apiKey": "{env:VIVGRID_API_KEY}"
      },
      "models": {
        "claude-fable-5-1": {
          "name": "claude-fable-5-1",
          "tool_call": true,
          "attachment": true,
          "modalities": { "input": ["text", "image"], "output": ["text"] },
          "limit": { "context": 1000000, "output": 128000 }
        }
      }
    }
  }
}

Export your key and launch OpenCode:

export VIVGRID_API_KEY="viv-xxxxxxxxxxxxx"
opencode

Use /models to switch between claude-fable-5-1 and other Vivgrid models mid-session. See the full OpenCode tutorial.

Pi

Install Pi:

npm install -g --ignore-scripts @earendil-works/pi-coding-agent

Add claude-fable-5-1 to a Vivgrid provider in ~/.pi/agent/models.json. Pi talks to Vivgrid over the native Messages API (/v1/messages) with "api": "anthropic-messages". authHeader sends the key as a Bearer token. Keep it as its own provider, since a provider has a single base URL and this one differs from the Chat Completions models':

{
  "providers": {
    "vivgrid-anthropic": {
      "baseUrl": "https://api.vivgrid.com",
      "apiKey": "viv-xxxxxxxxxxxxx",
      "authHeader": true,
      "api": "anthropic-messages",
      "models": [
        {
          "id": "claude-fable-5-1",
          "input": ["text", "image"],
          "contextWindow": 1000000,
          "maxTokens": 128000
        }
      ]
    }
  }
}

Make it the model Pi starts with in ~/.pi/agent/settings.json:

{
  "defaultProvider": "vivgrid-anthropic",
  "defaultModel": "claude-fable-5-1"
}

Then verify and start Pi:

pi --list-models vivgrid-anthropic
pi

Or run a one-shot prompt without entering the TUI:

pi -p "explain the auth flow in this repo" --model vivgrid-anthropic/claude-fable-5-1

See the full Pi tutorial.

API surfaces

The Vivgrid Console catalogs claude-fable-5-1 on 2 surfaces, all behind the same API key. The endpoint shown is the one the Console previews for that surface.

Quick start

Get an API key from the Vivgrid Console, then call claude-fable-5-1 directly.

curl https://api.vivgrid.com/v1/chat/completions \
  -H "Authorization: Bearer $VIVGRID_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-fable-5-1",
    "messages": [
      { "role": "user", "content": "Say hello in English, Chinese and Spanish." }
    ],
    "stream": true
  }'

curl https://api.vivgrid.com/v1/messages \
  -H "Authorization: Bearer $VIVGRID_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-fable-5-1",
    "max_tokens": 1024,
    "messages": [
      { "role": "user", "content": "Say hello in English, Chinese and Spanish." }
    ],
    "stream": true
  }'

Choosing within the Claude 5 family

Prices are USD per 1M tokens at the base rate. Rows marked this page are the model described here.

Ideal use cases

• Long-horizon coding agents that run for many turns without supervision
• Whole-repository migrations and refactors inside a single 1M-token pass
• High-stakes reasoning where answer quality outweighs token cost
• Deep research and analysis chaining many tool calls per session

Related models

• claude-fable-5 — the prior Fable release at the same per-token price
• claude-opus-5-5 — the latest Opus model at a lower price
• gpt-6-astra — OpenAI's frontier gpt-6 coding model