Observed

Source-reviewed Feb–Mar 2026: on Bedrock/Vertex, model: opus in agent frontmatter resolved to the hardcoded dated ID claude-opus-4-1-20250805 — not the live alias target — producing hard 400 errors when the org allowlist excluded that model, and ANTHROPIC_MODEL did not override it (#22587, #25530, #27754). Re-checked against the live tracker 2026-06-11: all three issues are now closed as stale or duplicate with no fix linked, so current frontmatter behavior is unverified in either direction. The label itself has since narrowed: the model-config page now documents that Bedrock, Vertex, and Foundry aliases resolve to older versions than the Anthropic API and instructs pinning via ANTHROPIC_DEFAULT_OPUS_MODEL.

1. UPDATE 2026-06-28(v2.1.195): the Bedrock/Vertex alias hardcoding is resolved — the model-config page now documents distinct per-provider targets (Opus 4.6 on Bedrock/Vertex vs Opus 4.8 on the Anthropic API) with ANTHROPIC_DEFAULT_OPUS_MODEL as a documented override; #22587/#25530 confirmed closed not-planned. Five new aliases added (best, fable, opusplan, sonnet[1m], opus[1m]). Residual per-provider version lag persists by design.