Claude streaming output sometimes truncated at end #6382

Summary

Intermittently, Claude-based models stream responses that are missing the last few characters/words. The stream ends cleanly (no visible error), but the final text delta never arrives.

This appears isolated to Claude providers; OpenAI / Gemini models do not seem to be affected.

Environment

• OpenCode: v1.0.207 (release commit 76880dce0)
• Runtime: Bun 1.3.5
• Claude via AI SDK: @ai-sdk/[email protected]

Reproduction

1. Configure any Claude model/provider.
2. Run a prompt with a strict sentinel at the end (repeat ~10 times):

Write 200 lines numbered 001–200.
Then write a final line exactly:
SENTINEL:'`’()[]{}<>✓Ω漢END
Do not output anything after END.

Expected

The final sentinel line always appears intact.

Actual

Occasionally the output ends early (mid-word / missing last characters). Examples include the final line being cut, e.g. SENTINEL:'\’`.

Investigation / suspected root cause

OpenCode consumes streamText().fullStream and appends each text-delta into the message; the TUI batches updates but flushes after stream end. This suggests OpenCode is not dropping the final chunk in its own aggregation/rendering.

OpenCode v1.0.207 pins @ai-sdk/anthropic to 2.0.50. In that version, the provider's doStream() uses ReadableStream.tee() and an un-awaited async IIFE to pull/cancel a "first chunk" branch while returning a delayed stream result. In some runtimes, canceling one tee branch while the other is still being consumed can prematurely end/disturb the underlying source, which can drop tail chunks. That would present exactly as "end-of-response truncation" with no explicit error.

@ai-sdk/[email protected] rewrites the first-chunk pulling logic to be synchronous/awaited and returns the consumer stream directly (no async IIFE / no DelayedPromise), which should remove this race.

Proposed fix (minimal)

Bump deps (staying within v2):

• @ai-sdk/anthropic: 2.0.50 → 2.0.56
• @ai-sdk/provider-utils: 3.0.18 → 3.0.19 (required by 2.0.56)

Patch:

diff --git a/packages/opencode/package.json b/packages/opencode/package.json
@@
-    "@ai-sdk/anthropic": "2.0.50",
+    "@ai-sdk/anthropic": "2.0.56",
@@
-    "@ai-sdk/provider-utils": "3.0.18",
+    "@ai-sdk/provider-utils": "3.0.19",

(and regenerate bun.lock)

I have this change ready on a branch and can open a PR if that’s the preferred workflow.