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OpenRouter proxy: tool calls silently dropped after AI SDK migration (tool-call event ignored) #11419
Description
Activity
Timeline correction
After tracing git history, the regression boundary described in this issue is inaccurate. The AI SDK was not present in v3.41.0 or v3.44.0, so neither version could have been affected by the
processAiSdkStreamPart()bug fixed in PR #11420.Actual timeline
Date Version Event Jan 15 v3.41.0 OpenRouter uses openaiSDK +NativeToolCallParser. No AI SDK. Works fine.Jan 20 — XML tool calling removed ( 8de9337e6, PR #10841)Jan 23 v3.42.0 First release without XML tools. OpenRouter still uses openaiSDK. Still works.Jan 27 v3.44.0 src/api/transform/ai-sdk.tsdoes not exist yet (created Jan 28 infe722dad2, PR #11047)Feb 6 v3.47.3 Latest numbered release. OpenRouter still uses openaiSDK.Feb 9 unreleased OpenRouter migrated to AI SDK ( 5773af8dd, PR #10778). This is whenprocessAiSdkStreamPart()became relevant to OpenRouter.Feb 11 unreleased PR #11420 fix lands Key findings
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src/api/transform/ai-sdk.tswas created on Jan 28 — 13 days after v3.41.0 and 1 day after v3.44.0. Neither version used this code path. -
OpenRouter used the plain
openainpm package at v3.41.0, streaming tool calls viaNativeToolCallParserwithdelta.tool_calls— a completely different code path. -
The OpenRouter AI SDK migration (PR feat: Refactor OpenRouter provider to use Vercel AI SDK #10778) landed Feb 9, after v3.47.3 (Feb 6). The bug can only manifest in unreleased builds or the next release.
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XML removal happened in v3.42.0 (Jan 23), not v3.44.0.
Corrected description
The true regression boundary is not v3.41.0 → v3.44.0. It is pre- vs post-OpenRouter AI SDK migration (PR #10778, Feb 9), which has not shipped in any numbered release. The fix in PR #11420 is correct — the issue description and title should be updated to reflect the actual regression boundary.
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- changed the title
[-]OpenRouter proxy: tool calls silently dropped after v3.41.0 (tool-call event ignored)[/-][+]OpenRouter proxy: tool calls silently dropped after AI SDK migration (tool-call event ignored)[/+]on Feb 12, 2026
Description
When using OpenRouter as a proxy, tool calls are silently dropped after the OpenRouter AI SDK migration (PR #10778, Feb 9), producing false "Model Response Incomplete / failed to use any tools" errors. This affects all models routed through OpenRouter and causes retry loops with significant cost inflation.
Root cause
Two interacting issues:
processAiSdkStreamPart()ignorestool-callevents (ai-sdk.ts line 491). The handler was designed to rely solely ontool-input-start/delta/endlifecycle events for tool delivery.@openrouter/ai-sdk-providerv2.1.1 has incomplete lifecycle emission:tool-input-start+tool-input-deltabut nevertool-input-endtool-callwith zerotool-input-*eventsThe combination means tool calls are silently lost. Prior to the AI SDK migration, OpenRouter used the
openainpm package withNativeToolCallParser, which handled tool calls correctly viadelta.tool_calls.Timeline
openaiSDK +NativeToolCallParser. Works fine.8de9337e6, PR #10841)openaiSDK. Still works.src/api/transform/ai-sdk.tsfirst created (fe722dad2, PR #11047)openaiSDK.The true regression boundary is the OpenRouter AI SDK migration (PR #10778, Feb 9), not v3.41.0 → v3.44.0 as originally stated.
Reproduction
Environment
Expected behavior
Tool calls routed through OpenRouter should be delivered and executed identically to direct provider connections.