FALLBACK_FOR_ALL_PRIMARY_MODELS

Updated October 13, 2026 by Alex Sorokoletov

FALLBACK_FOR_ALL_PRIMARY_MODELS is a Claude Code environment variable: Enable fallback for all primary models. Its release history is not tracked here. It is listed in the official reference.

How to set it

For one session, export it in the shell that starts Claude Code:

export FALLBACK_FOR_ALL_PRIMARY_MODELS=<value>
claude

To apply it to every session, add it to the env object of a settings file:

// ~/.claude/settings.json
{
  "env": {
    "FALLBACK_FOR_ALL_PRIMARY_MODELS": "<value>"
  }
}

Related variables

• CLAUDE_CODE_DISABLE_MODEL_ACCESS_FALLBACK: Present in the v2.1.285 build and absent from that release's notes.
• CLAUDE_CODE_NO_MODEL_FALLBACK: When set, the availability chain collapses to [primary]: buildAvailabilityFallbackChain() returns only the model you selected, and a tripwire error fires if any path still attempts a fallback pivot ("a model-fallback pivot was attempted while the no-fallback guarantee is active … this branch should be unreachable").
• ANTHROPIC_CUSTOM_MODEL_OPTION
• ANTHROPIC_CUSTOM_MODEL_OPTION_DESCRIPTION
• ANTHROPIC_CUSTOM_MODEL_OPTION_NAME
• ANTHROPIC_CUSTOM_MODEL_OPTION_SUPPORTED_CAPABILITIES
• ANTHROPIC_DEFAULT_FABLE_MODEL
• ANTHROPIC_DEFAULT_FABLE_MODEL_DESCRIPTION

Frequently asked questions

All variables, searchable: Claude Code environment variables.