---
title: "Claude Fable 5 with OrchestKit"
description: "How OrchestKit supports Claude Fable 5: correct pricing, a spend-consent gate for agent pins, advisor warnings, and the deliberate opt-in path (ORK_FABLE_OK)."
canonical: "https://orchestkit.yonyon.ai/docs/guides/claude-fable-5"
---

# Claude Fable 5 with OrchestKit

How OrchestKit supports Claude Fable 5: correct pricing, a spend-consent gate for agent pins, advisor warnings, and the deliberate opt-in path (ORK_FABLE_OK).

# Claude Fable 5 with OrchestKit

Claude Fable 5 (`claude-fable-5`, released 2026-06-09) is Anthropic's Mythos-class frontier model: state-of-the-art on coding, vision, and knowledge work, with week-long autonomous-run capability and a 1M-context variant (`claude-fable-5[1m]`). It bills at **$10 input / $50 output per MTok** — 2x Opus 4.8 output pricing — and in under 5% of sessions a safety classifier transparently falls back to Opus 5 (cyber/bio topics; you are informed when it happens).

OrchestKit supports Fable 5 fully, while treating it as a **deliberate spend decision** rather than a default.

> **Dated note (availability changes as capacity scales — verify current plan terms):** As announced 2026-07-18, beginning **July 20, 2026** Fable 5 is included in all **Max** and **Team Premium** plans at **50% of limits**. **Pro** and **Team Standard** users keep Fable access via usage credits and receive a one-time **$100 credit**. Anthropic has extended and reshaped access several times while securing capacity, so treat any specific inclusion/limit as point-in-time. Everything below is evergreen.

## What OrchestKit does for you

| Surface | Behavior |
|---------|----------|
| Pricing | `claude-fable-5` (+ `fable` alias and the `[1m]` variant) is priced correctly in cost estimation — previously unknown models silently fell back to sonnet pricing, underbilling by ~70% |
| Model vocabulary | One source of truth (`src/hooks/src/lib/models.vocab.json`) feeds agent-frontmatter validation, docs generation, the skill content lint, and pricing — `model: fable` is a first-class, CI-validated value |
| Spend consent | Spawning an agent **pinned** to fable triggers a permission prompt with the cost spelled out — approve per-spawn, or pre-consent with `ORK_FABLE_OK=1` |
| Cost advice | An agent that merely *inherits* fable from your session gets a downgrade warning when its task is low/medium complexity (~70%/60% savings vs. sonnet, derived from real pricing) |
| Tier rules | `fable` joins `opus` as a premium tier: CI reserves it for high-complexity agents (security/safety/system-design/event-driven/workflow) |

## Choosing where Fable 5 runs

There are three distinct decisions, and OrchestKit treats them differently:

1. **Your session model** (`/model`) — entirely yours; OrchestKit never interferes. `inherit` agents follow it.
2. **An agent pinned to fable** (`model: fable` in a spawn or agent frontmatter) — this commits future runs to frontier pricing, so the spend-consent gate asks first.
3. **Pre-consented automation** — set `ORK_FABLE_OK=1` in the environment (or CI) when you have deliberately decided a workload is worth frontier pricing.

```bash
# One-off: approve the permission prompt when it appears.
# Session/CI-wide pre-consent:
export ORK_FABLE_OK=1
```

The cost-neutral default for agent fleets is `model: inherit` — quality follows whatever you chose for the session (including fable when *you* chose it), prompt-cache forking keeps working, and nothing is silently committed to frontier pricing.

## Fallback behavior to know about

Fable 5's safety classifiers fall back to Opus 5 in a small fraction of sessions, most likely on cyber/bio-adjacent content. For security-audit workloads this means a fable-pinned auditor could silently switch models mid-run — one reason OrchestKit keeps its own security agents on an explicit `opus` pin rather than fable.

## Requirements

- Claude Code **2.1.220+** (OrchestKit's support floor) — Fable 5 access shipped in CC 2.1.170.
- No OrchestKit configuration is needed for any of the above; it ships in the `ork` plugin.