Beta header rewrite breaks Opus 5.5, Sonnet 5.5 and Fable 5.1 on OpenCode 1.18.x

[balaji-dutt]

On AI assistance: Claude (Opus 5.5 / 1M context) helped me narrow down the behavior and draft the wording below, including the repro steps. The actual issue and workflow are mine. — @balaji-dutt

Summary

With opencode 1.18.31 and opencode-claude-bridge 1.10.12, every request to a Claude 5.1+ model through the anthropic provider fails:

thinking.adaptive.block_binding: Extra inputs are not permitted

Since anomalyco/opencode#46653 (scoped to 5.1+ by anomalyco/opencode#46848), opencode adds thinking.block_binding to these requests and sends the thinking-binding-controls-2026-08-01 beta with it. buildBetaFlags() ignores the incoming anthropic-beta value and replaces it with BETA_FLAGS, so the field reaches the API without its beta.

#32 fixes this by merging the incoming flags. I'm filing this so the error is searchable, and to ask for #32 to be merged and released.

Affected models

Reproduced 2026-10-02 on macOS arm64, opencode 1.18.31 (Homebrew), bridge 1.10.12 (npm):

Model	Result
anthropic/claude-opus-5-5	400, error above
anthropic/claude-sonnet-5-5	400, error above
anthropic/claude-fable-5-1	400, error above
anthropic/claude-opus-5	OK (opencode sends no binding below 5.1)

Repro:

opencode run -m anthropic/claude-opus-5-5 'Reply with exactly: OK'

Confirming the cause

Adding the beta to the bridge's own list makes the same request succeed over OAuth, so the subscription path accepts it once it survives the rewrite:

ANTHROPIC_BETA_FLAGS="interleaved-thinking-2025-05-14,thinking-token-count-2026-05-13,context-management-2025-06-27,prompt-caching-scope-2026-01-05,claude-code-20250219,advisor-tool-2026-03-01,effort-2025-11-24,extended-cache-ttl-2025-04-11,thinking-binding-controls-2026-08-01" \
  opencode run -m anthropic/claude-opus-5-5 'Reply with exactly: OK'
# OK

Workaround

The per-model opt-out from anomalyco/opencode#46820, repeated for each 5.1+ model:

"provider": { "anthropic": { "models": {
  "claude-opus-5-5": { "options": { "thinking": { "type": "adaptive", "blockBinding": false } } }
} } }

Keep type: "adaptive". Without it, opencode drops the thinking object, and THINKING_MODELS only re-adds thinking for 4.x models, so the request goes out with no thinking at all.

Ask

Please merge and release #32. A release would also ship the #19 loader fix from #27: npm latest is still 1.10.12 (2026-07-02), and on 1.18.31 every start still logs failed to load plugin ... modelId.match is not a function. The request rewriting still runs despite that error; the ANTHROPIC_BETA_FLAGS test above changes the outcome.