diff --git a/docs/TELEMETRY.md b/docs/TELEMETRY.md
index 7e86f2779..9133aaf55 100644
--- a/docs/TELEMETRY.md
+++ b/docs/TELEMETRY.md
@@ -15,7 +15,7 @@ Three events, each with a small set of properties:
 | `inference_turn` | Once per completed turn | `provider_id`, `model_id`, `input_tokens`, `output_tokens`, `cache_read_tokens`, `cache_write_tokens`, `thinking_tokens`, `duration_ms` |
 
 Common properties attached to every event: a random installation UUID
-(`distinct_id`), `service_version`, `os_type`, `os_arch`, and a
+(`distinct_id`), `session_id`, `service_version`, `os_type`, `os_arch`, and a
 `schema_version` for forward compatibility.
 
 Approximate country-level location is derived server-side by PostHog from the
@@ -81,6 +81,11 @@ first run and stored in `~/.corbits/settings.json`. It identifies an
 installation, not a person — there is no account, email, or other PII behind
 it.
 
+`session_id` is a separate random UUID minted fresh each time the CLI
+process starts; it lives only in memory and is never written to disk or to
+`~/.corbits/settings.json`. It lets events be correlated within a single run
+and cannot be used to link one run to another.
+
 ## Backend
 
 Events are sent to PostHog. PostHog derives an approximate country from the
diff --git a/src/telemetry/index.ts b/src/telemetry/index.ts
index c1901a328..ba61adcc9 100644
--- a/src/telemetry/index.ts
+++ b/src/telemetry/index.ts
@@ -1,3 +1,5 @@
+import { randomUUID } from "node:crypto";
+
 import pkg from "../../package.json" with { type: "json" };
 import { ENV_PREFIX } from "../branding.js";
 import type { Settings } from "../config/settings.js";
@@ -26,10 +28,22 @@ export const TELEMETRY_NOTICE =
 
 export type TelemetryEvent = "cli_start" | "session_end" | "inference_turn";
 
+// One id per interactive process (TUI session or CLI invocation), generated
+// once at module load and reused by every createTelemetry() instance for the
+// life of the process — including across the toggle handler's re-creation on
+// enable/disable — so PostHog can group every event this process emits into
+// one session. Future emitters (AI turn events, feedback) read this via
+// getSessionId() rather than generating their own.
+const SESSION_ID = randomUUID();
+
+export function getSessionId(): string {
+  return SESSION_ID;
+}
+
 // Per-event property allowlist. Anything not listed here is stripped before
 // the payload leaves the process. Together with the fixed common properties
-// capture() appends (service_version, os_type, os_arch, schema_version),
-// this bounds everything telemetry can ever contain.
+// capture() appends (service_version, os_type, os_arch, schema_version,
+// session_id), this bounds everything telemetry can ever contain.
 const EVENT_PROPERTY_ALLOWLIST: Record<TelemetryEvent, readonly string[]> = {
   cli_start: [],
   session_end: ["status", "turn_count", "duration_ms", "session_mode", "exit_reason"],
@@ -140,6 +154,7 @@ export function createTelemetry(options: CreateTelemetryOptions): Telemetry {
         os_type: process.platform,
         os_arch: process.arch,
         schema_version: 1,
+        session_id: SESSION_ID,
       },
     };
 
diff --git a/tests/unit/telemetry-toggle.test.ts b/tests/unit/telemetry-toggle.test.ts
index 1e4fb541a..bd5e95f5a 100644
--- a/tests/unit/telemetry-toggle.test.ts
+++ b/tests/unit/telemetry-toggle.test.ts
@@ -1,6 +1,6 @@
 import { test, expect } from "bun:test";
 import { createTelemetryToggleHandler, type TelemetryToggleDeps } from "../../src/telemetry/toggle.js";
-import { createTelemetry } from "../../src/telemetry/index.js";
+import { createTelemetry, getSessionId } from "../../src/telemetry/index.js";
 import type { Settings } from "../../src/config/settings.js";
 import type { Telemetry } from "../../src/telemetry/index.js";
 
@@ -178,3 +178,39 @@ test("toggle on re-enables after settings load/save resolve", async () => {
   expect(saved?.telemetry?.enabled).toBe(true);
   expect(getInstance().enabled).toBe(true);
 });
+
+test("session_id on captured payloads stays constant across an enable/disable/enable toggle cycle", async () => {
+  const capturedBodies: { properties: Record<string, unknown> }[] = [];
+  const fetchFn = ((_url: string, init: RequestInit) => {
+    capturedBodies.push(JSON.parse(init.body as string));
+    return Promise.resolve(new Response("1", { status: 200 }));
+  }) as unknown as typeof fetch;
+  const { deps, getInstance } = fakeDeps({
+    createTelemetry: (opts) =>
+      createTelemetry({ ...opts, env: opts.env ?? {}, apiKey: opts.apiKey ?? "test-key", fetchFn }),
+  });
+  const handler = createTelemetryToggleHandler("/fake/path", deps);
+
+  // Re-enable once up front so the captured instance is one built through
+  // deps.createTelemetry (and thus fetchFn) rather than fakeDeps' bootstrap
+  // instance, which is wired to its own separate fetch counter.
+  handler(true);
+  await new Promise((resolve) => setTimeout(resolve, 10));
+  getInstance().capture("cli_start");
+
+  handler(false);
+  await new Promise((resolve) => setTimeout(resolve, 10));
+  getInstance().capture("cli_start"); // disabled: no fetch, but proves the swapped instance is live
+
+  handler(true);
+  await new Promise((resolve) => setTimeout(resolve, 10));
+  getInstance().capture("cli_start");
+
+  await new Promise((resolve) => setTimeout(resolve, 0));
+  expect(capturedBodies.length).toBe(2);
+  const sessionId = capturedBodies[0].properties.session_id;
+  expect(typeof sessionId).toBe("string");
+  expect((sessionId as string).length).toBeGreaterThan(0);
+  expect(capturedBodies[1].properties.session_id).toBe(sessionId);
+  expect(sessionId).toBe(getSessionId());
+});
diff --git a/tests/unit/telemetry.test.ts b/tests/unit/telemetry.test.ts
index af2cc8ba1..a34bfd48d 100644
--- a/tests/unit/telemetry.test.ts
+++ b/tests/unit/telemetry.test.ts
@@ -2,7 +2,12 @@ import { test, expect } from "bun:test";
 import { mkdtemp, rm } from "node:fs/promises";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
-import { createTelemetry, resolveTelemetryEnabled, telemetryDisabledByEnv } from "../../src/telemetry/index.js";
+import {
+  createTelemetry,
+  getSessionId,
+  resolveTelemetryEnabled,
+  telemetryDisabledByEnv,
+} from "../../src/telemetry/index.js";
 import { ensureTelemetrySettings } from "../../src/config/settings.js";
 import type { Settings } from "../../src/config/settings.js";
 
@@ -240,6 +245,30 @@ test("flush resolves immediately when nothing is pending", async () => {
   await expect(telemetry.flush()).resolves.toBeUndefined();
 });
 
+test("capture attaches the same session_id across multiple events in one process", async () => {
+  const calls: unknown[] = [];
+  const impl = ((_url: string, init: RequestInit) => {
+    calls.push(JSON.parse(init.body as string));
+    return Promise.resolve(new Response("1", { status: 200 }));
+  }) as unknown as typeof fetch;
+  const telemetry = createTelemetry({
+    settings: settingsWith("my-install-id"),
+    env: {},
+    fetchFn: impl,
+    apiKey: "test-key",
+  });
+  telemetry.capture("cli_start");
+  telemetry.capture("session_end", { status: "ok" });
+  await new Promise((resolve) => setTimeout(resolve, 0));
+  expect(calls.length).toBe(2);
+  const bodies = calls as { properties: Record<string, unknown> }[];
+  const sessionId = bodies[0].properties.session_id;
+  expect(typeof sessionId).toBe("string");
+  expect((sessionId as string).length).toBeGreaterThan(0);
+  expect(bodies[1].properties.session_id).toBe(sessionId);
+  expect(sessionId).toBe(getSessionId());
+});
+
 test("ensureTelemetrySettings called twice keeps installationId and enabled flag unchanged", async () => {
   const dir = await mkdtemp(join(tmpdir(), "corbits-telemetry-settings-"));
   const path = join(dir, "settings.json");