Source Intelligence

DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

All of v2.1.98 Home All releases olderv2.1.97 v2.1.100newer
Claude Code v2.1.98

Vertex AI Model Upgrade and Fallback System

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  • On startup (for first-party Vertex users), Claude Code checks whether pinned model versions are outdated compared to built-in defaults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_check and tengu_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.

See this entry in the whole of v2.1.98 →