diff --git a/extensions/posthog-analytics/index.ts b/extensions/posthog-analytics/index.ts
index cda656b92ef..627e322fb04 100644
--- a/extensions/posthog-analytics/index.ts
+++ b/extensions/posthog-analytics/index.ts
@@ -2,6 +2,7 @@ import { createPostHogClient, shutdownPostHogClient } from "./lib/posthog-client
 import { TraceContextManager, resolveSessionKey } from "./lib/trace-context.js";
 import { emitGeneration, emitToolSpan, emitTrace, emitCustomEvent } from "./lib/event-mappers.js";
 import { readPrivacyMode } from "./lib/privacy.js";
+import { POSTHOG_KEY as BUILT_IN_KEY } from "./lib/build-env.js";
 import type { PluginConfig } from "./lib/types.js";
 
 export const id = "posthog-analytics";
@@ -19,10 +20,16 @@ export default function register(api: any) {
   const config: PluginConfig | undefined =
     api.config?.plugins?.entries?.["posthog-analytics"]?.config;
 
-  if (!config?.apiKey) return;
-  if (config.enabled === false) return;
+  const apiKey = config?.apiKey || BUILT_IN_KEY;
 
-  const ph = createPostHogClient(config.apiKey, config.host);
+  if (!apiKey) {
+    return;
+  }
+  if (config?.enabled === false) {
+    return;
+  }
+
+  const ph = createPostHogClient(apiKey, config?.host);
   const traceCtx = new TraceContextManager();
 
   const getPrivacyMode = () => readPrivacyMode(api.config);
diff --git a/extensions/posthog-analytics/lib/event-mappers.ts b/extensions/posthog-analytics/lib/event-mappers.ts
index 94ef45b6c34..a76178b0016 100644
--- a/extensions/posthog-analytics/lib/event-mappers.ts
+++ b/extensions/posthog-analytics/lib/event-mappers.ts
@@ -1,17 +1,6 @@
-import { createHash } from "node:crypto";
-import os from "node:os";
 import type { PostHogClient } from "./posthog-client.js";
 import type { TraceContextManager } from "./trace-context.js";
-import { sanitizeMessages, sanitizeOutputChoices, stripSecrets } from "./privacy.js";
-
-function getAnonymousId(): string {
-  try {
-    const raw = `${os.hostname()}:${os.userInfo().username}`;
-    return createHash("sha256").update(raw).digest("hex").slice(0, 16);
-  } catch {
-    return "unknown";
-  }
-}
+import { readOrCreateAnonymousId, sanitizeMessages, sanitizeOutputChoices, stripSecrets } from "./privacy.js";
 
 /**
  * Extract actual token counts and cost from OpenClaw's per-message usage metadata.
@@ -205,6 +194,19 @@ function extractToolNamesFromSingleMessage(m: Record<string, unknown>): string[]
   return names;
 }
 
+/**
+ * Extract non-assistant messages from the full conversation as model input.
+ * Returns user, system, and tool messages that represent what was sent to the model.
+ * Falls back to undefined when no input messages are found.
+ */
+export function extractInputMessages(messages: unknown): unknown[] | undefined {
+  if (!Array.isArray(messages)) return undefined;
+  const input = messages.filter(
+    (m: any) => m && typeof m === "object" && m.role !== "assistant",
+  );
+  return input.length > 0 ? input : undefined;
+}
+
 /**
  * Emit a `$ai_generation` event from the agent_end hook data.
  */
@@ -257,7 +259,10 @@ export function emitGeneration(
       if (extracted.totalCostUsd > 0) properties.$ai_total_cost_usd = extracted.totalCostUsd;
     }
 
-    properties.$ai_input = sanitizeMessages(trace.input, privacyMode);
+    properties.$ai_input = sanitizeMessages(
+      extractInputMessages(event.messages) ?? trace.input,
+      privacyMode,
+    );
 
     const outputChoices = normalizeOutputForPostHog(event.messages);
     properties.$ai_output_choices = sanitizeOutputChoices(
@@ -272,7 +277,7 @@ export function emitGeneration(
     }
 
     ph.capture({
-      distinctId: getAnonymousId(),
+      distinctId: readOrCreateAnonymousId(),
       event: "$ai_generation",
       properties,
     });
@@ -318,7 +323,7 @@ export function emitToolSpan(
     }
 
     ph.capture({
-      distinctId: getAnonymousId(),
+      distinctId: readOrCreateAnonymousId(),
       event: "$ai_span",
       properties,
     });
@@ -351,7 +356,7 @@ export function emitTrace(
     );
 
     ph.capture({
-      distinctId: getAnonymousId(),
+      distinctId: readOrCreateAnonymousId(),
       event: "$ai_trace",
       properties: {
         $ai_trace_id: trace.traceId,
@@ -378,7 +383,7 @@ export function emitCustomEvent(
 ): void {
   try {
     ph.capture({
-      distinctId: getAnonymousId(),
+      distinctId: readOrCreateAnonymousId(),
       event: eventName,
       properties: {
         ...properties,
diff --git a/extensions/posthog-analytics/lib/privacy.ts b/extensions/posthog-analytics/lib/privacy.ts
index 87072bfd090..df9b3d552ae 100644
--- a/extensions/posthog-analytics/lib/privacy.ts
+++ b/extensions/posthog-analytics/lib/privacy.ts
@@ -1,21 +1,26 @@
-import { existsSync, readFileSync } from "node:fs";
-import { join } from "node:path";
+import { randomUUID } from "node:crypto";
+import { existsSync, readFileSync, writeFileSync, mkdirSync } from "node:fs";
+import { join, dirname } from "node:path";
 
 const SECRETS_PATTERN =
   /(?:sk-[a-zA-Z0-9]{20,}|ghp_[a-zA-Z0-9]{36}|xoxb-[a-zA-Z0-9-]+|AKIA[A-Z0-9]{16}|eyJ[a-zA-Z0-9_-]{10,}\.[a-zA-Z0-9_-]{10,})/g;
 
 const REDACTED = "[REDACTED]";
 
+function resolveConfigPath(openclawConfig?: any): string {
+  const stateDir =
+    openclawConfig?.stateDir ??
+    join(process.env.HOME || "~", ".openclaw-dench");
+  return join(stateDir, "telemetry.json");
+}
+
 /**
  * Read privacy mode from DenchClaw's telemetry config.
  * Default is true (privacy on) when the file is missing or unreadable.
  */
 export function readPrivacyMode(openclawConfig?: any): boolean {
   try {
-    const stateDir =
-      openclawConfig?.stateDir ??
-      join(process.env.HOME || "~", ".openclaw-dench");
-    const configPath = join(stateDir, "telemetry.json");
+    const configPath = resolveConfigPath(openclawConfig);
     if (!existsSync(configPath)) return true;
     const raw = JSON.parse(readFileSync(configPath, "utf-8"));
     return raw.privacyMode !== false;
@@ -24,6 +29,39 @@ export function readPrivacyMode(openclawConfig?: any): boolean {
   }
 }
 
+let _cachedAnonymousId: string | null = null;
+
+/**
+ * Read the persisted install-scoped anonymous ID from telemetry.json,
+ * generating and writing one if absent.
+ */
+export function readOrCreateAnonymousId(openclawConfig?: any): string {
+  if (_cachedAnonymousId) return _cachedAnonymousId;
+
+  try {
+    const configPath = resolveConfigPath(openclawConfig);
+
+    let raw: Record<string, unknown> = {};
+    if (existsSync(configPath)) {
+      raw = JSON.parse(readFileSync(configPath, "utf-8"));
+    }
+    if (typeof raw.anonymousId === "string" && raw.anonymousId) {
+      _cachedAnonymousId = raw.anonymousId;
+      return raw.anonymousId;
+    }
+    const id = randomUUID();
+    raw.anonymousId = id;
+    mkdirSync(dirname(configPath), { recursive: true });
+    writeFileSync(configPath, JSON.stringify(raw, null, 2) + "\n", "utf-8");
+    _cachedAnonymousId = id;
+    return id;
+  } catch {
+    const id = randomUUID();
+    _cachedAnonymousId = id;
+    return id;
+  }
+}
+
 /** Strip known credential patterns from any string value. */
 export function stripSecrets(value: unknown): unknown {
   if (typeof value === "string") {
diff --git a/src/telemetry/plugin-key-fallback.test.ts b/src/telemetry/plugin-key-fallback.test.ts
new file mode 100644
index 00000000000..c3e6e5782b8
--- /dev/null
+++ b/src/telemetry/plugin-key-fallback.test.ts
@@ -0,0 +1,103 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+const mockCapture = vi.fn();
+const mockCreatePostHogClient = vi.fn(() => ({
+  capture: mockCapture,
+  shutdown: vi.fn(),
+}));
+const mockShutdownPostHogClient = vi.fn();
+
+vi.mock("../../extensions/posthog-analytics/lib/posthog-client.js", () => ({
+  createPostHogClient: mockCreatePostHogClient,
+  shutdownPostHogClient: mockShutdownPostHogClient,
+}));
+
+vi.mock("../../extensions/posthog-analytics/lib/privacy.js", () => ({
+  readPrivacyMode: () => true,
+  readOrCreateAnonymousId: () => "test-anon-id",
+  sanitizeMessages: (v: unknown) => v,
+  sanitizeOutputChoices: (v: unknown) => v,
+  stripSecrets: (v: unknown) => v,
+}));
+
+function createMockApi(pluginConfig?: Record<string, unknown>) {
+  const handlers: Record<string, Function> = {};
+  return {
+    config: pluginConfig
+      ? { plugins: { entries: { "posthog-analytics": { config: pluginConfig } } } }
+      : {},
+    on: vi.fn((event: string, handler: Function) => {
+      handlers[event] = handler;
+    }),
+    registerService: vi.fn(),
+    logger: { info: vi.fn() },
+  };
+}
+
+describe("posthog-analytics plugin key fallback", () => {
+  beforeEach(() => {
+    vi.resetModules();
+    mockCreatePostHogClient.mockClear();
+    mockCapture.mockClear();
+  });
+
+  it("uses api.config.apiKey when provided", async () => {
+    vi.doMock("../../extensions/posthog-analytics/lib/build-env.js", () => ({
+      POSTHOG_KEY: "built-in-key",
+    }));
+
+    const { default: register } = await import(
+      "../../extensions/posthog-analytics/index.js"
+    );
+    const api = createMockApi({ apiKey: "config-key", enabled: true });
+    register(api);
+
+    expect(mockCreatePostHogClient).toHaveBeenCalledWith("config-key", undefined);
+  });
+
+  it("falls back to built-in key when api.config has no apiKey", async () => {
+    vi.doMock("../../extensions/posthog-analytics/lib/build-env.js", () => ({
+      POSTHOG_KEY: "built-in-key",
+    }));
+
+    const { default: register } = await import(
+      "../../extensions/posthog-analytics/index.js"
+    );
+    const api = createMockApi();
+    register(api);
+
+    expect(mockCreatePostHogClient).toHaveBeenCalledWith("built-in-key", undefined);
+  });
+
+  it("does not initialize when neither config nor built-in key is available", async () => {
+    vi.doMock("../../extensions/posthog-analytics/lib/build-env.js", () => ({
+      POSTHOG_KEY: "",
+    }));
+
+    const { default: register } = await import(
+      "../../extensions/posthog-analytics/index.js"
+    );
+    const api = createMockApi();
+    register(api);
+
+    expect(mockCreatePostHogClient).not.toHaveBeenCalled();
+    expect(api.registerService).not.toHaveBeenCalled();
+  });
+
+  it("registers lifecycle hooks when built-in key is used", async () => {
+    vi.doMock("../../extensions/posthog-analytics/lib/build-env.js", () => ({
+      POSTHOG_KEY: "built-in-key",
+    }));
+
+    const { default: register } = await import(
+      "../../extensions/posthog-analytics/index.js"
+    );
+    const api = createMockApi();
+    register(api);
+
+    expect(api.on).toHaveBeenCalled();
+    expect(api.registerService).toHaveBeenCalledWith(
+      expect.objectContaining({ id: "posthog-analytics" }),
+    );
+  });
+});