Mastra•2mo ago

Help: Cannot stream anything from workflows after recent update

Setup:

FE:
```
useChat
```
```
useChat
```
hook calling Fastify endpoint
BE: Custom endpoint using
```
run.streamVNext({ inputData })
```
run.streamVNext({ inputData })
```
run.streamVNext({ inputData })
```
run.streamVNext({ inputData })
then
```
toAISdkFormat(workflowStream, { from: 'workflow' })
```
toAISdkFormat(workflowStream, { from: 'workflow' })
```
toAISdkFormat(workflowStream, { from: 'workflow' })
```
toAISdkFormat(workflowStream, { from: 'workflow' })
Versions:
```
@mastra/core@0.23.3
```
@mastra/core@0.23.3
```
@mastra/core@0.23.3
```
@mastra/core@0.23.3
,
```
@mastra/ai-sdk@0.2.5
```
@mastra/ai-sdk@0.2.5
```
@mastra/ai-sdk@0.2.5
```
@mastra/ai-sdk@0.2.5

My workflow step:

execute: async ({ mastra, writer, ... }) => {
  const agent = mastra?.getAgent('generalInquiryAgent');
  const stream = await agent?.stream(messages, { runtimeContext });
  await stream!.textStream.pipeTo(writer!); // Text goes to workflow writer
  return { textResponse: await stream!.text };
}

execute: async ({ mastra, writer, ... }) => {
  const agent = mastra?.getAgent('generalInquiryAgent');
  const stream = await agent?.stream(messages, { runtimeContext });
  await stream!.textStream.pipeTo(writer!); // Text goes to workflow writer
  return { textResponse: await stream!.text };
}

execute: async ({ mastra, writer, ... }) => {
  const agent = mastra?.getAgent('generalInquiryAgent');
  const stream = await agent?.stream(messages, { runtimeContext });
  await stream!.textStream.pipeTo(writer!); // Text goes to workflow writer
  return { textResponse: await stream!.text };
}

execute: async ({ mastra, writer, ... }) => {
  const agent = mastra?.getAgent('generalInquiryAgent');
  const stream = await agent?.stream(messages, { runtimeContext });
  await stream!.textStream.pipeTo(writer!); // Text goes to workflow writer
  return { textResponse: await stream!.text };
}

My endpoint:

const workflowStream = await run.streamVNext({ inputData: { messages, userData } });
const aiSdkStream = toAISdkFormat(workflowStream, { from: 'workflow' });
return createUIMessageStreamResponse({ stream: aiSdkStream });

const workflowStream = await run.streamVNext({ inputData: { messages, userData } });
const aiSdkStream = toAISdkFormat(workflowStream, { from: 'workflow' });
return createUIMessageStreamResponse({ stream: aiSdkStream });

const workflowStream = await run.streamVNext({ inputData: { messages, userData } });
const aiSdkStream = toAISdkFormat(workflowStream, { from: 'workflow' });
return createUIMessageStreamResponse({ stream: aiSdkStream });

const workflowStream = await run.streamVNext({ inputData: { messages, userData } });
const aiSdkStream = toAISdkFormat(workflowStream, { from: 'workflow' });
return createUIMessageStreamResponse({ stream: aiSdkStream });

The problem:

toAISdkFormat

toAISdkFormat

toAISdkFormat

toAISdkFormat with

from: 'workflow'

from: 'workflow'

from: 'workflow'

from: 'workflow' only emits

data-workflow

data-workflow

data-workflow

data-workflow events (workflow metadata). The text I pipe via

writer.write()

writer.write()

writer.write()

writer.write() shows up in

workflow-step-output

workflow-step-output

workflow-step-output

workflow-step-output within those

data-workflow

data-workflow

data-workflow

data-workflow payloads, but it's never extracted into

text-delta

text-delta

text-delta

text-delta events that

useChat

useChat

expects.

Without writing hundreds of lines of manual stream transformation code to parse

data-workflow

data-workflow

data-workflow

data-workflow events and extract text from nested

workflow-step-output

workflow-step-output

workflow-step-output

workflow-step-output, I can't get text streaming to work. This feels like it should "just work" - I'm using the recommended

toAISdkFormat

toAISdkFormat

toAISdkFormat

toAISdkFormat utility and piping agent text to the workflow writer as shown in the docs.

Question:
Is there a built-in option/flag/way to get

text-delta

text-delta

text-delta

text-delta events from workflow text output? Or is manual transformation the only path forward? If manual, what's the recommended/simplest approach?

Asaf from SequenceOP•11/2/25, 2:05 PM

adding context from my debugging sessions with Claude. Perhaps it will help:

Mastra Workflow Text Streaming Issue - Quick Summary

The Problem

toAISdkFormat

toAISdkFormat

with

from: 'workflow'

from: 'workflow'

only emits

data-workflow

data-workflow

events (workflow metadata), not

text-delta

text-delta

events that

useChat

useChat

expects for streaming text.

Root Cause

In @mastra/ai-sdk/dist/index.js@mastra/ai-sdk/dist/index.js, the transformWorkflowtransformWorkflow function has a switch statement that handles:

workflow-startworkflow-start
workflow-step-startworkflow-step-start
workflow-step-resultworkflow-step-result
workflow-finishworkflow-finish
```
workflow-step-output
```
```
workflow-step-output
```
(falls to default: return nulldefault: return null
- gets discarded!)

When agent text is piped via

writer.write()

writer.write()

in workflow steps, it emits

workflow-step-output

workflow-step-output

chunks, but transformWorkflowtransformWorkflow ignores them completely.

What We Tried

```
from: 'workflow'
```
```
from: 'workflow'
```
- Only emits metadata, no text
from: 'agent'from: 'agent'
- Works perfectly BUT requires bypassing workflow (loses orchestration)
Manual transformation - User explicitly doesn't want this

## The Question

Is there a built-in way to get
text-delta
text-delta
events from workflow streams?

Or is the only option to:

Use agent directly (lose workflow orchestration), OR

Add manual transformation to extract

workflow-step-output

workflow-step-output

→

text-delta

text-delta

Versions:

@mastra/core@0.23.3

@mastra/core@0.23.3

, @mastra/ai-sdk@0.2.1@mastra/ai-sdk@0.2.1

Technical Details

Raw workflow stream emits perfect chunks:

type: 'workflow-step-output'
payload: { output: "text chunk here" }

type: 'workflow-step-output'
payload: { output: "text chunk here" }

But

toAISdkFormat

toAISdkFormat

with

from: 'workflow'

from: 'workflow'

transforms them into:

type: 'data-workflow'
data: { steps: {...}, output: null }

type: 'data-workflow'
data: { steps: {...}, output: null }

The fix needed in transformWorkflowtransformWorkflow:

case "workflow-step-output": {
  if (payload.payload?.output && typeof payload.payload.output === 'string') {
    return {
      type: "text-delta",
      id: payload.runId,
      delta: payload.payload.output
    };
  }
  return null;
}

case "workflow-step-output": {
  if (payload.payload?.output && typeof payload.payload.output === 'string') {
    return {
      type: "text-delta",
      id: payload.runId,
      delta: payload.payload.output
    };
  }
  return null;
}

But this case doesn't exist in the current implementation.

Mastra Triager•11/3/25, 12:05 PM

Created GitHub issue: https://github.com/mastra-ai/mastra/issues/9633

GitHub

[DISCORD:1434525854628577320] Help: Cannot stream anything from wor...

This issue was created from Discord post: https://discord.com/channels/1309558646228779139/1434525854628577320 Setup: FE: useChat hook calling Fastify endpoint BE: Custom endpoint using run.streamV...

Asaf from SequenceOP•11/5/25, 12:06 PM

Hey @Romain, is there an ETA on this? I really have to write a lot of code and "fake" streaming to make it work. Is there a workaround on how to properly stream text from workflows

Ward•11/5/25, 2:37 PM

We need to think about it a little, cause not everyone wants text-delta

Ward•11/5/25, 2:38 PM

we can expose an option to the workflow route and the transformer to pipe text-delta?

Ward•11/5/25, 2:41 PM

you could also manually do this

await stream!.textStream.pipeTo(new WritableStream({
  write(chunk) {
    writer.custom(chunk)
  },
}));

await stream!.textStream.pipeTo(new WritableStream({
  write(chunk) {
    writer.custom(chunk)
  },
}));

Asaf from SequenceOP•11/5/25, 3:17 PM

Thanks @Ward, I'll try it. but basically, we have a workflow that is nested and it generates a message to the user. Isn't the default behaviour being that writing text from any step should propegate and be sent to the user?

Asaf from SequenceOP•11/5/25, 3:19 PM

It's just not clear from the docs how to actually stream data from nested workflows. We have so much custom code to handle this that I'm honestly worried how it'll behave when there's a version bump. I really love what you guys are doing, but this is preventing us from actually deploying our app for several weeks now after a super painful migration process.

Wouldn't you guys want to see what's our setup and what challanges we are facing?

I'm really happy to share so many problems we are facing and still choosing to use Mastra as our go to stack, but I can't truly ship this with confidence unfortunately

Asaf from SequenceOP•11/5/25, 3:28 PM

Also, just tried your suggestion and I'm getting an error that custom is not a property of writer

Ward•11/5/25, 3:47 PM

100% !! can you reach out to @Shane (@mastra) (shane@mastra.ai)

Ward•11/5/25, 3:47 PM

would love to hear what you are building and improve our setup!

Ward•11/5/25, 3:47 PM

mmh @Asaf from Sequence what version of mastra core are you on?

Asaf from SequenceOP•11/5/25, 4:09 PM

I was on 0.21, updating to 0.23 seemed to fix the issue, but I need to go back to my stream parser to try to make it work. Reached out to @Shane (@mastra) as well, thanks!

Ariel•11/8/25, 9:40 PM

@Ward I'm trying to figure out how to stream text chunks from an agent call inside a workflow step using params.writerparams.writer

I've tried:

using the writer.customwriter.custom to emit the chunks directly from the fullStreamfullStream of the agent
using writer.writewriter.write to emit them the same way
tried the same with a toAiSdkFormattoAiSdkFormat stream

are you able to provide a quick snippet to help me understand how to achieve this?

I'm trying to just serve a workflowRouteworkflowRoute in my Mastra instance.

I can

console.log

console.log

the chunks and see the text chunks, but they don't stream on to the client.

Ariel•11/8/25, 9:44 PM

I'm speculating that because it's a workflowRouteworkflowRoute it just filters out text-related chunks, but if that's the case, I don't think this should be the behavior. Running agents in workflwos is pretty common, and for some of those we want to output text to the end user. I don't see an option to provide workflowworkflow to

chatRoute

chatRoute

. I'm confused here.

Ariel•11/8/25, 9:45 PM

FWIW, data-data- prefixed events processed correctly, but I specifically need the text parts.

gorpacrate•11/9/25, 3:39 AM

I'm carrying this bun patchbun patch with me through several latest mastra versions.

Already mentioned this in another thread – WorkflowStreamToAISDKTransformerWorkflowStreamToAISDKTransformer silently swallows "workflow-step-output""workflow-step-output" chunks - thus we are not receiving updates in the stream.

I'm not sure this is the correct fix ideologically – but at least it keeps me going.

diff --git a/dist/index.js b/dist/index.js
index d7ff3568bffeb712efd66387be28451c7f53a004..e384c5f983ff67fdf4796edf0f801a146a96944d 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -423,6 +423,24 @@ function WorkflowStreamToAISDKTransformer() {
       });
     },
     transform(chunk, controller) {
+      if (chunk.type === "workflow-step-output") {
+        const part = convertMastraChunkToAISDKv5({ chunk: chunk.payload.output, mode: "stream" });
+        if (part) {
+          const uiChunk = convertFullStreamChunkToUIMessageStream({
+            part,
+            sendReasoning: true,
+            sendSources: true,
+            sendStart: false,
+            sendFinish: false,
+            responseMessageId: chunk.runId,
+            onError() {
+              return "Error";
+            }
+          });
+          if (uiChunk) controller.enqueue(uiChunk);
+        }
+        return;
+      }
       const transformed = transformWorkflow(chunk, bufferedWorkflows);
       if (transformed) controller.enqueue(transformed);
     }

diff --git a/dist/index.js b/dist/index.js
index d7ff3568bffeb712efd66387be28451c7f53a004..e384c5f983ff67fdf4796edf0f801a146a96944d 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -423,6 +423,24 @@ function WorkflowStreamToAISDKTransformer() {
       });
     },
     transform(chunk, controller) {
+      if (chunk.type === "workflow-step-output") {
+        const part = convertMastraChunkToAISDKv5({ chunk: chunk.payload.output, mode: "stream" });
+        if (part) {
+          const uiChunk = convertFullStreamChunkToUIMessageStream({
+            part,
+            sendReasoning: true,
+            sendSources: true,
+            sendStart: false,
+            sendFinish: false,
+            responseMessageId: chunk.runId,
+            onError() {
+              return "Error";
+            }
+          });
+          if (uiChunk) controller.enqueue(uiChunk);
+        }
+        return;
+      }
       const transformed = transformWorkflow(chunk, bufferedWorkflows);
       if (transformed) controller.enqueue(transformed);
     }

This way I just normally stream with toAISdkFormat

const run = workflow.createRunAsync(...);
const stream = run.resumeStream(...);
return toAISdkFormat(stream, { from: "workflow" });

const run = workflow.createRunAsync(...);
const stream = run.resumeStream(...);
return toAISdkFormat(stream, { from: "workflow" });

And inside workflow step it's just

const result = await agent.stream(...);
await result.fullstream.pipeTo(writer);

const result = await agent.stream(...);
await result.fullstream.pipeTo(writer);

Asaf from SequenceOP•11/9/25, 12:34 PM

Thanks @gorpacrate. Again, ideally streaming shuold just work out of the box. Let's wait for @Ward or @roamin

Ward•11/20/25, 2:19 PM

Hi, we are looking into these issues and fixing

The one mentioned above should be fixed.

For streaming text from workflow, we will add a new argument that you can add to the workflow route

Ward•11/26/25, 8:18 AM

@Asaf from Sequence did you manage to test it without your bun patch?