CLAUDE_CODE_NO_MODEL_FALLBACK
Updated by Alex Sorokoletov
CLAUDE_CODE_NO_MODEL_FALLBACK is a Claude Code environment variable: 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"). Added between v2.1.212 and v2.1.215 and still present in v2.1.294. It is not in the official reference.
| Status | Present in v2.1.294 |
|---|---|
| Added | Added between v2.1.212 and v2.1.215 |
| Category | Models and thinking |
| Official docs | Not listed |
How to set it
For one session, export it in the shell that starts Claude Code:
export CLAUDE_CODE_NO_MODEL_FALLBACK=<value>
claudeTo apply it to every session, add it to the env object of a settings file:
// ~/.claude/settings.json
{
"env": {
"CLAUDE_CODE_NO_MODEL_FALLBACK": "<value>"
}
}Release notes that mention it
- Claude Code Version Tracker: Undocumented Env Vars, Feature Gates & Models
- claude-code-env-vars-v2-1-215
Related variables
CLAUDE_CODE_DISABLE_MODEL_ACCESS_FALLBACK: Present in the v2.1.285 build and absent from that release's notes.ANTHROPIC_CUSTOM_MODEL_OPTIONANTHROPIC_CUSTOM_MODEL_OPTION_DESCRIPTIONANTHROPIC_CUSTOM_MODEL_OPTION_NAMEANTHROPIC_CUSTOM_MODEL_OPTION_SUPPORTED_CAPABILITIESANTHROPIC_DEFAULT_FABLE_MODELANTHROPIC_DEFAULT_FABLE_MODEL_DESCRIPTIONANTHROPIC_DEFAULT_FABLE_MODEL_NAME
Frequently asked questions
What does CLAUDE_CODE_NO_MODEL_FALLBACK do?
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").
Which Claude Code version has CLAUDE_CODE_NO_MODEL_FALLBACK?
Added between v2.1.212 and v2.1.215 and still present in v2.1.294.
How do I set CLAUDE_CODE_NO_MODEL_FALLBACK?
Export it before starting Claude Code (export CLAUDE_CODE_NO_MODEL_FALLBACK=value), or add it to the "env" object in ~/.claude/settings.json to apply it to every session.
All variables, searchable: Claude Code environment variables.