[dinwwwh]

Summary

AI SDK tools get a default toModelOutput, modeled on how the MCP integration maps outputs:

• Outputs are serialized like OpenAPI responses (OpenAPIJsonSerializer). Date, BigInt, Set, Map and similar types now reach the model as JSON. Before, the AI SDK's own JSON round trip turned Set/Map into {}, and a BigInt made it throw.
• Blob/File outputs, nested or not, are sent as file content.
  • A top-level file becomes a single file part with its MIME type and file name.
  • Nested files are sent as the JSON text plus one file part each, named by path (for example files/0/q3.pdf).
  • File data is base64-encoded once, so providers don't re-encode the bytes on every step.
• A new serializer option on implementToolFactory / createToolFactory lets you share custom types with an OpenAPI handler, the same as McpRegistrar's option.
• You can still take over: toModelOutput set in tool options or aiSdkTool meta overrides the default.

@orpc/openapi becomes a runtime dependency of @orpc/ai-sdk, for the serializer, as it already is for @orpc/mcp.

The TODO about adding a JSON Schema converter option is removed: tools keep leaving JSON Schema conversion to the AI SDK.

Notes

• toModelOutput only shapes what the model receives. The AI SDK still streams and stores the raw tool output, so a BigInt output can still fail UI streaming, and history rebuilt from saved UI messages loses non-JSON values and files.
• A ReadableStream output still reaches the model as {}, as with the AI SDK's own default.

Testing

• New tests cover serialization, top-level and nested files, the serializer option, override precedence, and an end-to-end generateText run showing the file part reach the tool message.
• pnpm vitest run packages/ai-sdk packages/openapi tests, the root tsc and the package type check, eslint, sherif and pnpm docs:validate pass.

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
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commit: e60d3b2

[codspeed]

Merging this PR will not alter performance

1 warning

⚠️ 5 benchmarks are dominated by system calls

System calls cannot be simulated consistently and are left out of the measure. The reported value understates the real cost. Switch to the Walltime instrument to measure them.

Learn more about system calls

See affected benchmarks

✅ 28 untouched benchmarks
⏩ 2 skipped benchmarks¹

---

_{Comparing claude/ai-sdk-tool-converters-mwqxlc (e60d3b2) with main (4c76597)}

Footnotes

1. 2 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩