feat(ai-ui-message-stream): client tools, structured output and reconnect for AI SDK routes by tombeckenham · Pull Request #1891 · TanStack/ai

tombeckenham · 2026-10-23T05:24:31Z

TanStack useChat now gets more from an AI SDK route than the AI SDK's own client: client tools that the route reads from the request, typed structured output, and reconnect backoff. Stacked on #1888.

🎯 Changes

Client-declared tools. fromChatTransport sends the client's tool declarations in the request body as clientTools. On the AI SDK route, clientToolsFromAISDKBody(body, serverTools) turns them into AI SDK tools without execute, so streamText stops at the call and the client runs it.
- Server tools win a name clash.
- A malformed clientTools throws.
- Browser WebMCP tools reach the route the same way.
Typed structured output. With outputSchema on fromChatTransport (the same schema as useChat({ outputSchema })), an Output.object answer becomes a structured-output part, with partial objects while it streams and a checked final value. A schema failure ends the run with RUN_ERROR.
Reconnect backoff. A dropped stream now reconnects with createReconnectTracker, the backoff and limits of the TanStack HTTP connections, set with the new reconnect option. @tanstack/ai-client exports createReconnectTracker and ReconnectTracker for this, and becomes a required peer of the bridge.
Proofs over the bridge. Tests show that client persistence, the message queue, devtools events and loading saved AI SDK chats (initialMessages: fromAISDKMessages(saved)) all work.
Docs. The client guide lists what the TanStack client gives against an AI SDK route, and adds sections for client tools on the route, structured output, saved chats and reconnect. The compatibility table, README and migration skill are updated.

✅ Checklist

I have followed the steps in the Contributing guide.
I have tested code changes locally with pnpm run test:pr, or these tests do not apply to this pull request.
I fully understand the code in this pull request, including any code generated with AI assistance.
Docs: I updated docs/ for this change, or this change is not user-facing.
Changeset: I added a changeset (pnpm changeset), or this PR does not change a published package.

🚀 Release Impact

This change affects published code, and I have generated a changeset.
This change is docs/CI/dev-only (no release).

Testing

Commands run

In packages/ai-ui-message-stream: vitest run (48 passed), test:types, test:oxlint, knip.
In packages/ai-client: test:types, test:oxlint. The one lint warning is in existing code.
kiira check on the changed docs and skill, and pnpm test:docs.
Not run locally: pnpm test:pr and the E2E suite. CI runs them.

Manual test

On an AI SDK route, use streamText({ tools: clientToolsFromAISDKBody(body, {}) }).
On the client, use useChat({ tools: [myClientTool], connection: fromChatTransport(new DefaultChatTransport({ api })) }).
Ask for something that needs the tool. The client runs it, and the route continues with its output.

How this PR makes testing easy

tests/client-tools.test.ts runs a real ChatClient, fromChatTransport and AI SDK streamText with a mock model.
tests/client-extras.test.ts covers structured output, the queue, devtools and saved chats.
tests/reconnect.test.ts covers backoff and the no-progress limit.

Risk / rollback

Low. Every option is new and off by default, except two changes:

Reconnect: it now retries with backoff up to the limit, instead of once.
Peer: @tanstack/ai-client is now a required peer of @tanstack/ai-ui-message-stream.

Revert the PR to undo both.

Public API change

Before: every client tool also had to be defined on the AI SDK route.

After

// AI SDK route
const body = await request.json()
const result = streamText({
  model,
  messages: await convertToModelMessages(body.messages),
  tools: clientToolsFromAISDKBody(body, { getWeather }),
})

// TanStack client
useChat({
  threadId,
  tools: [getLocation],
  outputSchema: recipe,
  connection: fromChatTransport(new DefaultChatTransport({ api: '/api/chat' }), {
    outputSchema: recipe,
    reconnect: { maxAttempts: 10 },
  }),
})

// @tanstack/ai-client
import { createReconnectTracker } from '@tanstack/ai-client'

…nect for AI SDK routes TanStack useChat gets more from an AI SDK route: - fromChatTransport sends the client's tool declarations in the request body. clientToolsFromAISDKBody(body, serverTools) turns them into AI SDK tools without execute on the route, so client and WebMCP tools need no copy there. Server tools win a name clash. - With outputSchema, an Output.object answer becomes a typed structured-output part with partial objects and a checked final value. - A dropped stream reconnects with createReconnectTracker, the backoff of the TanStack HTTP connections, set with the reconnect option. @tanstack/ai-client now exports createReconnectTracker. Tests prove client persistence, the message queue, devtools and loading saved AI SDK chats over the bridge.

changeset-bot · 2026-10-23T05:24:35Z

🦋 Changeset detected

Latest commit: a576436

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@tanstack/ai-ui-message-stream	Minor
@tanstack/ai-client	Patch
ag-ui	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

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…ctured output

nx-cloud · 2026-10-23T05:26:38Z

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☁️ Nx Cloud last updated this comment at 2026-10-23 05:28:11 UTC

github-actions · 2026-10-23T05:28:29Z

Coverage

✅ Coverage held across 10 compared package(s).

Each package is measured twice in this job — on this PR and on its merge-base with main — and compared. A metric fails only when it is at or above 60% on the merge-base and under 60% on this PR. Other drops are listed but do not fail. Packages your PR doesn't affect are not measured and not listed.

package	statements	branches	functions	lines
ai-angular	73.83% (0.00)	60.89% (0.00)	61.83% (0.00)	75.40% (0.00)	ok
ai-client	87.81% (0.00)	79.97% (0.00)	87.01% (0.00)	90.13% (0.00)	ok
ai-octane	91.19% (0.00)	68.26% (0.00)	87.44% (0.00)	91.47% (0.00)	ok
ai-preact	86.50% (0.00)	71.00% (0.00)	87.50% (0.00)	87.98% (0.00)	ok
ai-react	81.94% (0.00)	65.42% (0.00)	80.73% (0.00)	82.67% (0.00)	ok
ai-remix	43.02% (0.00)	30.35% (0.00)	39.02% (0.00)	46.23% (0.00)	ok
ai-solid	75.81% (0.00)	57.63% (0.00)	71.28% (0.00)	78.11% (0.00)	ok
ai-svelte	74.05% (0.00)	50.99% (0.00)	70.05% (0.00)	78.64% (0.00)	ok
ai-ui-message-stream	87.78% (+0.89)	80.29% (+1.08)	94.11% (+2.05)	89.55% (+0.92)	ok
ai-vue	73.33% (0.00)	48.73% (0.00)	73.28% (0.00)	74.66% (0.00)	ok

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commit: a576436

tombeckenham added this pull request to stack #1892 October 23, 2026 05:24

docs(ai-ui-message-stream): note that text in a tool step breaks stru…

a576436

…ctured output

tombeckenham removed this pull request from stack #1892 October 23, 2026 07:51

tombeckenham merged commit a576436 into ag-ui-adapter Oct 23, 2026
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tombeckenham deleted the ag-ui-adapter-client branch October 23, 2026 07:51

This was referenced Oct 23, 2026

feat(ai-ui-message-stream): bridge TanStack AI and the AI SDK UI message stream #1888

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feat(ai-ui-message-stream): client tools, structured output and reconnect for AI SDK routes - #1891

feat(ai-ui-message-stream): client tools, structured output and reconnect for AI SDK routes#1891
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