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,toolsDetails
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 pickerANTHROPIC_DEFAULT_FABLE_MODEL_DESCRIPTION— description shown alongside the modelANTHROPIC_DEFAULT_FABLE_MODEL_SUPPORTED_CAPABILITIES— capabilities string for the modelVERTEX_REGION_CLAUDE_FABLE_5— region override for Fable 5 on Vertex AI (same pattern as the existingVERTEX_REGION_CLAUDE_*vars)- When
ANTHROPIC_DEFAULT_FABLE_MODELis 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_MODELto your Fable 5 model ID andANTHROPIC_DEFAULT_OPUS_MODELto 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.