diff --git a/README.md b/README.md
index df5a920..7c36d83 100644
--- a/README.md
+++ b/README.md
@@ -18,6 +18,7 @@ Build AI agent teams that decompose goals into tasks automatically. Define agent
 - **Model Agnostic** — Claude, GPT, Gemma 4, and local models (Ollama, vLLM, LM Studio) in the same team. Swap models per agent via `baseURL`.
 - **Structured Output** — Add `outputSchema` (Zod) to any agent. Output is parsed as JSON, validated, and auto-retried once on failure. Access typed results via `result.structured`.
 - **Task Retry** — Set `maxRetries` on tasks for automatic retry with exponential backoff. Failed attempts accumulate token usage for accurate billing.
+- **Observability** — Optional `onTrace` callback emits structured spans for every LLM call, tool execution, task, and agent run — with timing, token usage, and a shared `runId` for correlation. Zero overhead when not subscribed, zero extra dependencies.
 - **In-Process Execution** — No subprocess overhead. Everything runs in one Node.js process. Deploy to serverless, Docker, CI/CD.
 
 ## Quick Start
@@ -120,6 +121,7 @@ npx tsx examples/01-single-agent.ts
 | [08 — Gemma 4 Local](examples/08-gemma4-local.ts) | `runTasks()` + `runTeam()` with local Gemma 4 via Ollama — zero API cost |
 | [09 — Structured Output](examples/09-structured-output.ts) | `outputSchema` (Zod) on AgentConfig — validated JSON via `result.structured` |
 | [10 — Task Retry](examples/10-task-retry.ts) | `maxRetries` / `retryDelayMs` / `retryBackoff` with `task_retry` progress events |
+| [11 — Trace Observability](examples/11-trace-observability.ts) | `onTrace` callback — structured spans for LLM calls, tools, tasks, and agents |
 
 ## Architecture
 
diff --git a/README_zh.md b/README_zh.md
index c9f7ac9..458d6de 100644
--- a/README_zh.md
+++ b/README_zh.md
@@ -18,6 +18,7 @@
 - **模型无关** — Claude、GPT、Gemma 4 和本地模型（Ollama、vLLM、LM Studio）可以在同一个团队中使用。通过 `baseURL` 即可接入任何 OpenAI 兼容服务。
 - **结构化输出** — 为任意智能体添加 `outputSchema`（Zod），输出自动解析为 JSON 并校验，校验失败自动重试一次。通过 `result.structured` 获取类型化结果。
 - **任务重试** — 为任务设置 `maxRetries`，失败时自动指数退避重试。所有尝试的 token 用量累计，确保计费准确。
+- **可观测性** — 可选的 `onTrace` 回调为每次 LLM 调用、工具执行、任务和智能体运行发出结构化 span 事件——包含耗时、token 用量和共享的 `runId` 用于关联追踪。未订阅时零开销，零额外依赖。
 - **进程内执行** — 没有子进程开销。所有内容在一个 Node.js 进程中运行。可部署到 Serverless、Docker、CI/CD。
 
 ## 快速开始
@@ -120,6 +121,7 @@ npx tsx examples/01-single-agent.ts
 | [08 — Gemma 4 本地](examples/08-gemma4-local.ts) | `runTasks()` + `runTeam()` 本地 Gemma 4 via Ollama — 零 API 费用 |
 | [09 — 结构化输出](examples/09-structured-output.ts) | `outputSchema`（Zod）— 校验 JSON 输出，通过 `result.structured` 获取 |
 | [10 — 任务重试](examples/10-task-retry.ts) | `maxRetries` / `retryDelayMs` / `retryBackoff` + `task_retry` 进度事件 |
+| [11 — 可观测性](examples/11-trace-observability.ts) | `onTrace` 回调 — LLM 调用、工具、任务、智能体的结构化 span 事件 |
 
 ## 架构
 
diff --git a/examples/11-trace-observability.ts b/examples/11-trace-observability.ts
new file mode 100644
index 0000000..20b463e
--- /dev/null
+++ b/examples/11-trace-observability.ts
@@ -0,0 +1,133 @@
+/**
+ * Example 11 — Trace Observability
+ *
+ * Demonstrates the `onTrace` callback for lightweight observability. Every LLM
+ * call, tool execution, task lifecycle, and agent run emits a structured trace
+ * event with timing data and token usage — giving you full visibility into
+ * what's happening inside a multi-agent run.
+ *
+ * Trace events share a `runId` for correlation, so you can reconstruct the
+ * full execution timeline. Pipe them into your own logging, OpenTelemetry, or
+ * dashboard.
+ *
+ * Run:
+ *   npx tsx examples/11-trace-observability.ts
+ *
+ * Prerequisites:
+ *   ANTHROPIC_API_KEY env var must be set.
+ */
+
+import { OpenMultiAgent } from '../src/index.js'
+import type { AgentConfig, TraceEvent } from '../src/types.js'
+
+// ---------------------------------------------------------------------------
+// Agents
+// ---------------------------------------------------------------------------
+
+const researcher: AgentConfig = {
+  name: 'researcher',
+  model: 'claude-sonnet-4-6',
+  systemPrompt: 'You are a research assistant. Provide concise, factual answers.',
+  maxTurns: 2,
+}
+
+const writer: AgentConfig = {
+  name: 'writer',
+  model: 'claude-sonnet-4-6',
+  systemPrompt: 'You are a technical writer. Summarize research into clear prose.',
+  maxTurns: 2,
+}
+
+// ---------------------------------------------------------------------------
+// Trace handler — log every span with timing
+// ---------------------------------------------------------------------------
+
+function handleTrace(event: TraceEvent): void {
+  const dur = `${event.durationMs}ms`.padStart(7)
+
+  switch (event.type) {
+    case 'llm_call':
+      console.log(
+        `  [LLM]   ${dur}  agent=${event.agent}  model=${event.model}  turn=${event.turn}` +
+        `  tokens=${event.tokens.input_tokens}in/${event.tokens.output_tokens}out`,
+      )
+      break
+    case 'tool_call':
+      console.log(
+        `  [TOOL]  ${dur}  agent=${event.agent}  tool=${event.tool}` +
+        `  error=${event.isError}`,
+      )
+      break
+    case 'task':
+      console.log(
+        `  [TASK]  ${dur}  task="${event.taskTitle}"  agent=${event.agent}` +
+        `  success=${event.success}  retries=${event.retries}`,
+      )
+      break
+    case 'agent':
+      console.log(
+        `  [AGENT] ${dur}  agent=${event.agent}  turns=${event.turns}` +
+        `  tools=${event.toolCalls}  tokens=${event.tokens.input_tokens}in/${event.tokens.output_tokens}out`,
+      )
+      break
+  }
+}
+
+// ---------------------------------------------------------------------------
+// Orchestrator + team
+// ---------------------------------------------------------------------------
+
+const orchestrator = new OpenMultiAgent({
+  defaultModel: 'claude-sonnet-4-6',
+  onTrace: handleTrace,
+})
+
+const team = orchestrator.createTeam('trace-demo', {
+  name: 'trace-demo',
+  agents: [researcher, writer],
+  sharedMemory: true,
+})
+
+// ---------------------------------------------------------------------------
+// Tasks — researcher first, then writer summarizes
+// ---------------------------------------------------------------------------
+
+const tasks = [
+  {
+    title: 'Research topic',
+    description: 'List 5 key benefits of TypeScript for large codebases. Be concise.',
+    assignee: 'researcher',
+  },
+  {
+    title: 'Write summary',
+    description: 'Read the research from shared memory and write a 3-sentence summary.',
+    assignee: 'writer',
+    dependsOn: ['Research topic'],
+  },
+]
+
+// ---------------------------------------------------------------------------
+// Run
+// ---------------------------------------------------------------------------
+
+console.log('Trace Observability Example')
+console.log('='.repeat(60))
+console.log('Pipeline: research → write (with full trace output)')
+console.log('='.repeat(60))
+console.log()
+
+const result = await orchestrator.runTasks(team, tasks)
+
+// ---------------------------------------------------------------------------
+// Summary
+// ---------------------------------------------------------------------------
+
+console.log('\n' + '='.repeat(60))
+console.log(`Overall success: ${result.success}`)
+console.log(`Tokens — input: ${result.totalTokenUsage.input_tokens}, output: ${result.totalTokenUsage.output_tokens}`)
+
+for (const [name, r] of result.agentResults) {
+  const icon = r.success ? 'OK  ' : 'FAIL'
+  console.log(`  [${icon}] ${name}`)
+  console.log(`         ${r.output.slice(0, 200)}`)
+}