What
Automatic detection of stale Vertex model pins and probing for accessible fallback models when defaults are unavailable.
Details
- On startup (for first-party Vertex users), Claude Code checks whether pinned model versions are outdated compared to built-in defaults
- For each stale tier, it probes Vertex AI to verify the upgrade candidate is accessible (one-token request, 20s timeout)
- If upgrades are found, presents a dialog to update model pins
- Separately, detects unpinned tiers where the default model may not be accessible and finds compatible fallbacks
- Displays warnings when fallback models are used instead of defaults
- Logs telemetry:
tengu_vertex_upgrade_checkandtengu_vertex_fallback_check - Auto-restarts Claude Code when model configuration changes
Evidence
Vertex upgrade/fallback system (search for "[vertex-upgrade] tiersWithPin=" and "[vertex-fallback] unpinnedTiers=")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.