Fable 5 Environment Variables for Custom Providers / Claude Code v2.1.170

What

Four new environment variables let BYOC (Bring Your Own Claude) and API-gateway deployments point Claude Code at a custom Fable 5 endpoint.

Usage

export ANTHROPIC_DEFAULT_FABLE_MODEL=my-fable-5-endpoint
export ANTHROPIC_DEFAULT_FABLE_MODEL_NAME="My Fable 5"
export ANTHROPIC_DEFAULT_FABLE_MODEL_DESCRIPTION="Custom Fable 5 model"
export ANTHROPIC_DEFAULT_FABLE_MODEL_SUPPORTED_CAPABILITIES=vision,tools

Details

ANTHROPIC_DEFAULT_FABLE_MODEL — custom Fable 5 model ID (enables the alias and fallback logic even on non-firstParty providers)
ANTHROPIC_DEFAULT_FABLE_MODEL_NAME — display name shown in the model picker
ANTHROPIC_DEFAULT_FABLE_MODEL_DESCRIPTION — description shown alongside the model
ANTHROPIC_DEFAULT_FABLE_MODEL_SUPPORTED_CAPABILITIES — capabilities string for the model
VERTEX_REGION_CLAUDE_FABLE_5 — region override for Fable 5 on Vertex AI (same pattern as the existing VERTEX_REGION_CLAUDE_* vars)
When ANTHROPIC_DEFAULT_FABLE_MODEL is set, Claude Code shows a "Custom Fable model" entry in the picker in place of the default Fable 5 entry (on non-firstParty providers)
A new fallback hint is also surfaced for providers where these vars are absent: "To enable automatic fallback on this provider, set ANTHROPIC_DEFAULT_FABLE_MODEL to your Fable 5 model ID and ANTHROPIC_DEFAULT_OPUS_MODEL to your Opus 4.8 model ID."

Evidence

Env var registration (search for "ANTHROPIC_DEFAULT_FABLE_MODEL") and custom-model picker entry (search for "Custom Fable model")

Strings lifted out of the shipped bundle, so the claim above can be checked against them.