assistant-ui Observability

Always consult assistant-ui.com/llms.txt for the latest API.

Tracing and telemetry for an assistant-ui backend. Most of this is generic AI SDK telemetry; the assistant-ui specific part is the route handler and the

@assistant-ui/react-o11y

client primitives for rendering spans.

References
Where it plugs in
Provider routing
AI SDK telemetry (shared)
Helicone (proxy, no OTel)
Visualizing spans with react-o11y
Common Gotchas
Related Skills

References

./references/langfuse.md -- Langfuse tracing
./references/langsmith.md -- LangSmith tracing
./references/helicone.md -- Helicone proxy
./references/react-o11y.md -- @assistant-ui/react-o11y client primitives

Where it plugs in

Telemetry attaches to the server route that calls

streamText

generateText

, not to the React runtime. The frontend (

useChatRuntime

Thread

) is unchanged.

react-o11y

is a separate, optional client layer for drawing the trace waterfall in your own UI.

Thread (frontend) ──> /api/chat (streamText) ──> tracing backend
                                              └─> react-o11y (optional UI)

Provider routing

Langfuse   → OTel span processor + experimental_telemetry, propagateAttributes
LangSmith  → wrapAISDK(ai) wrapper, no OTel setup
Helicone   → proxy baseURL on the provider, no telemetry flag
react-o11y → client primitives to render spans you collected

AI SDK telemetry (shared)

Langfuse and any OTel backend reuse the AI SDK

experimental_telemetry

flag. Enable it per call:

import { openai } from "@ai-sdk/openai";
import { streamText, convertToModelMessages } from "ai";
import type { UIMessage } from "ai";

export async function POST(req: Request) {
  const { messages }: { messages: UIMessage[] } = await req.json();
  const result = streamText({
    model: openai("gpt-5.4-nano"),
    messages: await convertToModelMessages(messages),
    experimental_telemetry: { isEnabled: true },
  });
  return result.toUIMessageStreamResponse();
}

For Langfuse, register an OTel span processor in

instrumentation.ts

and wrap the call so traces carry

userId

sessionId

import { NodeSDK } from "@opentelemetry/sdk-node";
import { LangfuseSpanProcessor } from "@langfuse/otel";

export const langfuseSpanProcessor = new LangfuseSpanProcessor();

export async function register() {
  if (process.env.NEXT_RUNTIME !== "nodejs") return;
  const sdk = new NodeSDK({ spanProcessors: [langfuseSpanProcessor] });
  sdk.start();
}

import { propagateAttributes } from "@langfuse/tracing";

const result = await propagateAttributes(
  { traceName: "chat-completion", userId, sessionId },
  async () =>
    streamText({
      model: openai("gpt-5.4-nano"),
      messages: await convertToModelMessages(messages),
      experimental_telemetry: { isEnabled: true },
    }),
);

LangSmith skips OTel entirely; wrap the

ai

module instead.

convertToModelMessages

is not wrapped, so import it from

ai

directly:

import * as ai from "ai";
import { wrapAISDK } from "langsmith/experimental/vercel";
import { openai } from "@ai-sdk/openai";

const { streamText } = wrapAISDK(ai);

const result = streamText({
  model: openai("gpt-5.4-nano"),
  messages: await ai.convertToModelMessages(messages),
});
return result.toUIMessageStreamResponse();

See the per provider reference files for env vars, metadata tagging, and serverless flushing.

Helicone (proxy, no OTel)

Helicone needs no telemetry flag. Point the provider at the proxy

baseURL

and pass the auth header:

import { createOpenAI } from "@ai-sdk/openai";

const openai = createOpenAI({
  baseURL: "https://oai.helicone.ai/v1",
  headers: { "Helicone-Auth": `Bearer ${process.env.HELICONE_API_KEY}` },
});

Use this

openai

instance with

streamText

as usual; streaming, tools, and attachments are unchanged.

Visualizing spans with react-o11y

@assistant-ui/react-o11y

gives headless primitives to render collected spans as a trace waterfall. Feed it

SpanData[]

(id, parentSpanId, name, type, status, startedAt, endedAt, latencyMs) via

SpanResource

, mount with

useAui

, and render

SpanPrimitive

parts.

bash

npm install @assistant-ui/react-o11y

tsx

import {
  SpanResource,
  SpanPrimitive,
  type SpanData,
} from "@assistant-ui/react-o11y";
import { AuiProvider, useAui } from "@assistant-ui/store";

function SpanRow() {
  return (
    <SpanPrimitive.Root>
      <SpanPrimitive.Indent />
      <SpanPrimitive.CollapseToggle />
      <SpanPrimitive.StatusIndicator />
      <SpanPrimitive.TypeBadge />
      <SpanPrimitive.Name />
    </SpanPrimitive.Root>
  );
}

export function TraceView({ spans }: { spans: SpanData[] }) {
  const aui = useAui({ resource: SpanResource({ spans }) });
  return (
    <AuiProvider value={aui}>
      <SpanPrimitive.Children components={{ Span: SpanRow }} />
    </AuiProvider>
  );
}

SpanPrimitive.Children

flattens the tree to a visible list and wraps each item in

SpanByIndexProvider

Root

exposes

data-span-status

data-span-type

data-span-depth

, and

data-collapsed

for styling. See react-o11y.md for the full part list and

SpanState

shape.

Common Gotchas

No traces on Vercel/Lambda

The function exits before OTel flushes its buffer. Langfuse:
```
await langfuseSpanProcessor.forceFlush()
```
before responding. LangSmith:
```
await new Client().awaitPendingTraceBatches()
```
.

Langfuse traces empty

experimental_telemetry: { isEnabled: true }

must be set on each

streamText

generateText

call.

The span processor only registers when
```
process.env.NEXT_RUNTIME === "nodejs"
```
; OTel does not run on the edge runtime.

LangSmith not tracing

Use the destructured methods from
```
wrapAISDK(ai)
```
, not the originals from
```
ai
```
.
```
LANGSMITH_TRACING=true
```
must be set.

Helicone requests still hit OpenAI directly

Confirm requests go to

oai.helicone.ai

, not

api.openai.com

, and carry both

Helicone-Auth

and

Authorization

headers.

react-o11y renders nothing

Primitives must render inside
```
AuiProvider
```
; the resource mounts through
```
useAui({ resource: SpanResource({ spans }) })
```
.

Related Skills

```
/streaming
```
- The route handler and stream response telemetry attaches to
```
/setup
```
- Backend wiring (
```
ai-sdk
```
,
```
custom-backend
```
) where the route lives
```
/cloud
```
- Persistence; pair
```
userId
```
/
```
sessionId
```
/
```
threadId
```
with trace attributes

observability

NPX Install

Tags

SKILL.md Content