Vertex AI's Anthropic endpoint rejects unknown anthropic-beta tokens with
HTTP 400. buildUpstreamRequestAnthropicVertex forwarded the client header
verbatim via the allowedHeaders whitelist, so recent Claude Code CLIs that
send advisor-tool-2026-03-01, prompt-caching-scope-2026-01-05,
redact-thinking-2026-02-12 and thinking-token-count-2026-05-13 broke every
Vertex service_account request, even though plain account-test requests passed.
This is the only upstream builder that bypassed beta filtering: the
OAuth/API-key path uses computeFinalAnthropicBeta and the Bedrock path uses
filterBedrockBetaTokens. Close the gap with a Vertex-specific whitelist
(vertexSupportedBetaTokens) mirroring bedrockSupportedBetaTokens, plus the
existing BetaPolicy block check:
- evaluateBetaPolicy block check (symmetric to resolveBedrockBetaTokensForRequest)
- filterVertexBetaTokens strips policy-filtered + non-whitelisted tokens
- body context_management sanitize now keys on the final beta, not the raw client value
- overwrite the anthropic-beta header after the whitelist copy loop with the final value
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
