AI SDK leaks Zod internal properties (_def, ZodEffects) into tool schema JSON

[SamirMahmudzade]

Description

Zod internal properties (_def, ZodEffects, "zod", "preprocess", _cached, _ctx) leak into the serialized tool/function declaration JSON schema sent to LLM APIs. This causes 400 Invalid JSON payload errors when using providers that strictly validate JSON Schema (Google Gemini, Anthropic Claude via strict proxies).

Error Example

[400]: Invalid JSON payload received. Unknown name "_def" at
'request.tools[0].function_declarations[3].parameters.properties[0].value':
Cannot find field.

Full error from Antigravity Manager (Anthropic SDK -> Gemini):

Invalid value at 'request.tools[0].function_declarations[3].parameters...
.properties[0].value.properties[0].value.properties[1].value.type', "preprocess"
Invalid value at 'request.tools[0].function_declarations[3].parameters...
.properties[0].value.properties[0].value.properties[2].value', "ZodEffects"

Affected Providers

All AI SDK provider packages share @ai-sdk/core:

• @ai-sdk/openai / @ai-sdk/openai-compatible -> same bug
• @ai-sdk/google -> same bug
• @ai-sdk/anthropic -> same bug

Working Providers

qw/* and cmd/* models (Qwen, GPT, DeepSeek, etc.) work because they accept extra fields silently.

Environment

• OpenCode Version: 1.14.33 (macOS .app bundle)
• AI SDK bundled inside: /Applications/OpenCode.app/Contents/Resources/app.asar/out/main/chunks/node-DlUV59aW.js
• Error Source: OpenAIResponsesLanguageModel3.doStream

Root Cause

@ai-sdk/core (bundled inside OpenCode.app) does not properly strip Zod internal properties when converting Zod schemas to JSON Schema for function declarations. The _def property and related Zod internals leak into the serialized payload. Updating the bundled AI SDK version should resolve this.

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Bug: Zod internal properties leak into JSON Schema sent to provider (Kimi k2.6) #28704: Same root cause — Zod internal properties (_def, ~standard, _cached, typeName) leaking into tool schema JSON sent to provider APIs, causing 400 errors. That report targets Kimi k2.6 but describes the identical serialization bug.
• experimental.ts uses zodToJsonSchema which is broken with Zod v4 #20807: Related — zodToJsonSchema broken with Zod v4, which is part of the same schema conversion pipeline.
• TypeError: undefined is not an object (evaluating 'schema2._zod.def') - zod v3/v4 conflict when plugins bundle zod v4 #21155: Related — Zod v3/v4 conflict causing _zod.def errors in plugin tool schemas.

If your issue is distinct from these (e.g. a different code path or provider-specific behavior not covered there), please add a comment explaining the difference so maintainers can track it separately.