[Feature]: Support Zod 4 in @ag-ui/mastra

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I have searched existing issues and this hasn't been requested yet.

Problem or Motivation

Following up on #1397 for the @ag-ui/mastra package specifically.

As of @ag-ui/mastra@1.1.4, its published package.json declares zod: "^3.25.76" as a dependency. Applications using Zod 4 therefore install a separate Zod 3 copy for the adapter.

This is becoming awkward when @ag-ui/mastra is used alongside libraries that require Zod 4. For example, @rekog/mcp-nest@2.x, a NestJS library for building MCP servers, declares zod: "^4.3.5" as a peer dependency. Downgrading the application's Zod version to 3.x causes npm dependency resolution to fail.

@mastra/client-js and @mastra/core already accept both Zod 3 and Zod 4 in their peer dependency ranges. It would be useful for the AG-UI Mastra adapter to support applications using Zod 4 as well.

Proposed Solution

Test @ag-ui/mastra against Zod 4 and update its dependency declaration to support Zod 4 if the adapter is compatible. If code changes are needed, it would be helpful to document what is required before the dependency range can be widened.

Could the related @ai-sdk/ui-utils dependency also be checked? An npm install with @ag-ui/mastra@1.1.4 can produce an ERESOLVE overriding peer dependency warning involving @mastra/client-js, @ai-sdk/ui-utils, and the nested Zod 3 copy. Updating the adapter's Zod range alone may not remove that warning.

Additional Context

Related broader request: #1397.

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@T0nete

Hey @T0nete, thanks for opening the issue. I've added support for Zod 4 to the roadmap.

Could the Zod 4 support here come "for free" by moving @ag-ui/mastra off @ai-sdk/ui-utils onto the current AI SDK?
(I asked my agent to do some summary thingies :) )

From what I can see on @ag-ui/mastra@1.1.4, the only thing pulling in @ai-sdk/ui-utils (and with it the pinned zod@^3.25.76) is a single import of a single function — parsePartialJson:
import { parsePartialJson } from "@ai-sdk/ui-utils";

@ai-sdk/ui-utils is an AI SDK v4-era package that peers zod@^3.23.8, so an app on Zod 4 ends up with a second, nested Zod 3 copy — which is the ERESOLVE overriding peer dependency warning mentioned above.

The same parsePartialJson is exported by the current AI SDK (the ai package, and @ai-sdk/provider-utils), which @mastra/core already depends on and which accepts zod@^3.25.0 || ^4.0.0. The return shape looks identical, with one difference I want to confirm:

// @ai-sdk/ui-utils (v4): synchronous
parsePartialJson(text): { value; state }

// ai / @ai-sdk/provider-utils (current): async
parsePartialJson(text): Promise<{ value; state }>

So the questions:

Is parsePartialJson the only reason @ai-sdk/ui-utils is a dependency, or does the adapter use anything else from it?
Would replacing that import with the one from the AI SDK already in the tree (and await-ing it at the one call site) be enough to drop @ai-sdk/ui-utils entirely — and in doing so let the Zod range widen to ^3.25.0 || ^4.0.0 (matching @mastra/core and @mastra/client-js)?
If it's not that simple, what else is in the way? (e.g. the sync→async change rippling into a sync stream-transform path, or a behavioral difference in the newer parsePartialJson.)

Also, would making zod a peer dependency (as proposed in #2518) rather than a pinned dependency be preferred here, so the host app controls the Zod version regardless of this specific swap?

fix(mastra): support Zod 4 by dropping @ai-sdk/ui-utils (ag-ui-protoc…

fix(mastra): vendor parsePartialJson and drop @ai-sdk/ui-utils (ag-ui…

#3224 fixes this. It drops @ai-sdk/ui-utils (the source of the nested Zod 3 copy) by vendoring a synchronous parsePartialJson, the same way Mastra did in mastra-ai/mastra#27297, and widens the adapter's zod range to ^3.25.76 || ^4.0.0. In a consumer install with Zod 4, the adapter now resolves the app's own Zod.

It supersedes #3007, which took the ai@5 route.

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[Feature]: Support Zod 4 in @ag-ui/mastra #2874

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[Feature]: Support Zod 4 in @ag-ui/mastra #2874

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NathanTarbert commented on Oct 2, 2026

sander-su commented on Oct 6, 2026

sander-su commented on Oct 27, 2026

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