observability

name	observability
description	Adds tracing, telemetry, and observability to an assistant-ui backend. Use when wiring an AI SDK route handler (streamText/generateText, toUIMessageStreamResponse) to a tracing backend: Langfuse via OpenTelemetry (LangfuseSpanProcessor and NodeSDK in instrumentation.ts, experimental_telemetry isEnabled, propagateAttributes with traceName/userId/sessionId, langfuseSpanProcessor.forceFlush on serverless), LangSmith via wrapAISDK(ai) from langsmith/experimental/vercel (createLangSmithProviderOptions, awaitPendingTraceBatches), or Helicone via createOpenAI baseURL https://oai.helicone.ai/v1 with the Helicone-Auth header. Also covers rendering collected spans with @assistant-ui/react-o11y headless primitives (SpanResource, SpanPrimitive Root/Indent/CollapseToggle/StatusIndicator/TypeBadge/Name/Children, SpanByIndexProvider, SpanData/SpanState) mounted via useAui/AuiProvider from @assistant-ui/store. Use for missing or empty traces, edge vs nodejs runtime telemetry, serverless flush issues, or trace waterfalls.
license	MIT

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.

Contents

• 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.

npm install @assistant-ui/react-o11y

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