diff --git a/mem0-ts/src/client/config.ts b/mem0-ts/src/client/config.ts
index 646360661..5ebd7faf2 100644
--- a/mem0-ts/src/client/config.ts
+++ b/mem0-ts/src/client/config.ts
@@ -3,7 +3,9 @@
  *
  * Used to stitch PostHog identities: SDKs and CLIs persist anonymous
  * distinct_id values here, and the TS MemoryClient reads those on init to
- * fire $identify and merge them into the email identity.
+ * fire $identify and merge them into the email identity. The OSS user_id is
+ * only a stitch candidate when telemetry.oss_used_at proves OSS Memory
+ * actually ran here (the platform client never mints ids itself).
  *
  * Node-only. Browsers (no `process.versions.node`) no-op.
  */
@@ -11,6 +13,7 @@
 export interface Mem0AnonIds {
   oss?: string;
   cli?: string;
+  ossUsedAt?: string;
   aliasedPairs: string[];
 }
 
@@ -110,6 +113,10 @@ export async function readMem0AnonIds(): Promise<Mem0AnonIds | null> {
       typeof telemetry.anonymous_id === "string"
         ? telemetry.anonymous_id
         : undefined,
+    ossUsedAt:
+      typeof telemetry.oss_used_at === "string" && telemetry.oss_used_at
+        ? telemetry.oss_used_at
+        : undefined,
     aliasedPairs: Array.isArray(telemetry.aliased_pairs)
       ? telemetry.aliased_pairs.filter(
           (item: unknown) => typeof item === "string",
@@ -137,6 +144,26 @@ export async function isMem0Aliased(
   return aliasedPairs.includes(aliasPairMarker(node, anonId, email));
 }
 
+export async function markMem0OssUsed(): Promise<void> {
+  const node = await getNodeFs();
+  if (!node) return;
+  try {
+    const config = loadConfig(node) ?? {};
+    const telemetry =
+      config.telemetry && typeof config.telemetry === "object"
+        ? config.telemetry
+        : {};
+    if (typeof telemetry.oss_used_at === "string" && telemetry.oss_used_at) {
+      return;
+    }
+    telemetry.oss_used_at = new Date().toISOString();
+    config.telemetry = telemetry;
+    writeConfig(node, config);
+  } catch {
+    // Best-effort: read-only filesystems and unwritable paths just skip.
+  }
+}
+
 export async function markMem0Aliased(
   anonId: string,
   email: string,
diff --git a/mem0-ts/src/client/mem0.ts b/mem0-ts/src/client/mem0.ts
index 89fe45cef..cbb315199 100644
--- a/mem0-ts/src/client/mem0.ts
+++ b/mem0-ts/src/client/mem0.ts
@@ -27,12 +27,7 @@ import {
   isTelemetryEnabled,
   telemetry,
 } from "./telemetry";
-import {
-  getOrCreateMem0UserId,
-  isMem0Aliased,
-  markMem0Aliased,
-  readMem0AnonIds,
-} from "./config";
+import { isMem0Aliased, markMem0Aliased, readMem0AnonIds } from "./config";
 import { camelToSnake, camelToSnakeKeys, snakeToCamelKeys } from "./utils";
 import { createExceptionFromResponse, MemoryError } from "../common/exceptions";
 
@@ -151,12 +146,16 @@ export default class MemoryClient {
     try {
       const email = this.telemetryId;
       if (!email || !email.includes("@")) return;
-      const sharedAnonId = await getOrCreateMem0UserId();
       const anonIds = await readMem0AnonIds();
-      if (!anonIds && !sharedAnonId) return;
-      const candidates = [anonIds?.oss || sharedAnonId, anonIds?.cli].filter(
-        (id): id is string => !!id && id !== email,
-      );
+      if (!anonIds) return;
+      // The OSS user_id is only a stitch candidate when telemetry.oss_used_at
+      // proves OSS Memory actually ran here; never mint an id from the
+      // platform client path. The CLI anon id is presence-based (only the
+      // CLIs write it).
+      const candidates = [
+        anonIds.ossUsedAt ? anonIds.oss : undefined,
+        anonIds.cli,
+      ].filter((id): id is string => !!id && id !== email);
       const seen = new Set<string>();
       for (const anonId of candidates) {
         if (seen.has(anonId) || (await isMem0Aliased(anonId, email))) continue;
diff --git a/mem0-ts/src/client/telemetry.ts b/mem0-ts/src/client/telemetry.ts
index df3a722d4..78bade1a2 100644
--- a/mem0-ts/src/client/telemetry.ts
+++ b/mem0-ts/src/client/telemetry.ts
@@ -85,6 +85,7 @@ class UnifiedTelemetry implements TelemetryClient {
       properties: {
         $anon_distinct_id: anonId,
         client_source: "typescript",
+        client_version: version,
         $lib: "posthog-node",
       },
     };
diff --git a/mem0-ts/src/client/tests/telemetry-aliasing.test.ts b/mem0-ts/src/client/tests/telemetry-aliasing.test.ts
index a0351bbf1..67b30fc86 100644
--- a/mem0-ts/src/client/tests/telemetry-aliasing.test.ts
+++ b/mem0-ts/src/client/tests/telemetry-aliasing.test.ts
@@ -13,6 +13,7 @@ import {
   getOrCreateMem0UserId,
   isMem0Aliased,
   markMem0Aliased,
+  markMem0OssUsed,
   readMem0AnonIds,
 } from "../config";
 import { TEST_API_KEY } from "./helpers";
@@ -145,6 +146,55 @@ describe("config.ts — readMem0AnonIds / markMem0Aliased", () => {
       markMem0Aliased("oss-uuid", "user@example.com"),
     ).resolves.toBeUndefined();
   });
+
+  test("markMem0OssUsed writes marker preserving other fields", async () => {
+    fs.writeFileSync(
+      path.join(tmpHome, "config.json"),
+      JSON.stringify({
+        user_id: "oss-uuid",
+        telemetry: { anonymous_id: "cli-anon", aliased_pairs: ["pair-marker"] },
+      }),
+    );
+    await markMem0OssUsed();
+    const written = JSON.parse(
+      fs.readFileSync(path.join(tmpHome, "config.json"), "utf8"),
+    );
+    expect(written.user_id).toBe("oss-uuid");
+    expect(written.telemetry.anonymous_id).toBe("cli-anon");
+    expect(written.telemetry.aliased_pairs).toEqual(["pair-marker"]);
+    expect(written.telemetry.oss_used_at).toBeTruthy();
+  });
+
+  test("markMem0OssUsed is idempotent", async () => {
+    await markMem0OssUsed();
+    const first = JSON.parse(
+      fs.readFileSync(path.join(tmpHome, "config.json"), "utf8"),
+    ).telemetry.oss_used_at;
+    await markMem0OssUsed();
+    const second = JSON.parse(
+      fs.readFileSync(path.join(tmpHome, "config.json"), "utf8"),
+    ).telemetry.oss_used_at;
+    expect(second).toBe(first);
+  });
+
+  test("readMem0AnonIds surfaces ossUsedAt", async () => {
+    fs.writeFileSync(
+      path.join(tmpHome, "config.json"),
+      JSON.stringify({
+        user_id: "oss-uuid",
+        telemetry: { oss_used_at: "2026-01-01T00:00:00.000Z" },
+      }),
+    );
+    const ids = await readMem0AnonIds();
+    expect(ids?.oss).toBe("oss-uuid");
+    expect(ids?.ossUsedAt).toBe("2026-01-01T00:00:00.000Z");
+  });
+
+  test("markMem0OssUsed does not throw when target dir is unwritable", async () => {
+    fs.writeFileSync(path.join(tmpHome, "blocker"), "x");
+    process.env.MEM0_DIR = path.join(tmpHome, "blocker"); // file used as dir
+    await expect(markMem0OssUsed()).resolves.toBeUndefined();
+  });
 });
 
 // ─── telemetry.captureIdentify ───────────────────────────────
@@ -166,6 +216,7 @@ describe("telemetry.captureIdentify", () => {
     expect(payload.event).toBe("$identify");
     expect(payload.distinct_id).toBe("user@example.com");
     expect(payload.properties.$anon_distinct_id).toBe("anon-uuid");
+    expect(payload.properties.client_version).toBeTruthy();
     expect(payload.properties.$process_person_profile).toBeUndefined();
   });
 
@@ -220,7 +271,10 @@ describe("MemoryClient — _maybeAliasAnonToEmail", () => {
   test("fires $identify on first init and persists pair marker", async () => {
     fs.writeFileSync(
       path.join(tmpHome, "config.json"),
-      JSON.stringify({ user_id: "oss-uuid" }),
+      JSON.stringify({
+        user_id: "oss-uuid",
+        telemetry: { oss_used_at: "2026-01-01T00:00:00.000Z" },
+      }),
     );
     const fetchMock = setupMockFetchWithPostHog();
 
@@ -244,17 +298,38 @@ describe("MemoryClient — _maybeAliasAnonToEmail", () => {
     expect(written.telemetry.aliased_pairs).toHaveLength(1);
   });
 
-  test("platform-first init creates shared anon ID and identifies it", async () => {
+  test("platform-only init mints nothing and fires no $identify", async () => {
+    // Regression: the client used to create the shared anon id itself and
+    // immediately stitch it, merging an event-less anon person into every
+    // platform user. The platform path must now be read-only.
     const fetchMock = setupMockFetchWithPostHog();
 
     const client = makeStubClient("test@example.com");
     await (client as any)._maybeAliasAnonToEmail();
 
-    const written = JSON.parse(
-      fs.readFileSync(path.join(tmpHome, "config.json"), "utf8"),
+    expect(fs.existsSync(path.join(tmpHome, "config.json"))).toBe(false);
+
+    const identifyCalls = (fetchMock.mock.calls as any[]).filter(
+      ([, init]: [string, RequestInit]) => {
+        if (!init?.body) return false;
+        return JSON.parse(init.body as string).event === "$identify";
+      },
     );
-    expect(written.user_id).toBeTruthy();
-    expect(written.telemetry.aliased_pairs).toHaveLength(1);
+    expect(identifyCalls.length).toBe(0);
+  });
+
+  test("oss id without oss_used_at marker is not stitched; cli id still is", async () => {
+    fs.writeFileSync(
+      path.join(tmpHome, "config.json"),
+      JSON.stringify({
+        user_id: "oss-uuid",
+        telemetry: { anonymous_id: "cli-anon" },
+      }),
+    );
+    const fetchMock = setupMockFetchWithPostHog();
+
+    const client = makeStubClient("test@example.com");
+    await (client as any)._maybeAliasAnonToEmail();
 
     const identifyCalls = (fetchMock.mock.calls as any[]).filter(
       ([, init]: [string, RequestInit]) => {
@@ -264,8 +339,32 @@ describe("MemoryClient — _maybeAliasAnonToEmail", () => {
     );
     expect(identifyCalls.length).toBe(1);
     const body = JSON.parse(identifyCalls[0][1].body);
-    expect(body.distinct_id).toBe("test@example.com");
-    expect(body.properties.$anon_distinct_id).toBe(written.user_id);
+    expect(body.properties.$anon_distinct_id).toBe("cli-anon");
+  });
+
+  test("stitches config written by the Python SDK (cross-SDK key compat)", async () => {
+    // Python writes datetime.now(timezone.utc).isoformat(): +00:00 offset.
+    fs.writeFileSync(
+      path.join(tmpHome, "config.json"),
+      JSON.stringify({
+        user_id: "oss-uuid",
+        telemetry: { oss_used_at: "2026-01-01T00:00:00+00:00" },
+      }),
+    );
+    const fetchMock = setupMockFetchWithPostHog();
+
+    const client = makeStubClient("test@example.com");
+    await (client as any)._maybeAliasAnonToEmail();
+
+    const identifyCalls = (fetchMock.mock.calls as any[]).filter(
+      ([, init]: [string, RequestInit]) => {
+        if (!init?.body) return false;
+        return JSON.parse(init.body as string).event === "$identify";
+      },
+    );
+    expect(identifyCalls.length).toBe(1);
+    const body = JSON.parse(identifyCalls[0][1].body);
+    expect(body.properties.$anon_distinct_id).toBe("oss-uuid");
   });
 
   test("second init does not refire $identify", async () => {
@@ -273,7 +372,7 @@ describe("MemoryClient — _maybeAliasAnonToEmail", () => {
       path.join(tmpHome, "config.json"),
       JSON.stringify({
         user_id: "oss-uuid",
-        telemetry: {},
+        telemetry: { oss_used_at: "2026-01-01T00:00:00.000Z" },
       }),
     );
     await markMem0Aliased("oss-uuid", "test@example.com");
@@ -296,7 +395,10 @@ describe("MemoryClient — _maybeAliasAnonToEmail", () => {
       path.join(tmpHome, "config.json"),
       JSON.stringify({
         user_id: "oss-uuid",
-        telemetry: { anonymous_id: "cli-anon" },
+        telemetry: {
+          anonymous_id: "cli-anon",
+          oss_used_at: "2026-01-01T00:00:00.000Z",
+        },
       }),
     );
     const fetchMock = setupMockFetchWithPostHog();
@@ -407,4 +509,18 @@ describe("config.ts in browser-like environment", () => {
       jest.resetModules();
     }
   });
+
+  test("markMem0OssUsed is a no-op when not Node", async () => {
+    const originalProcess = global.process;
+    // @ts-expect-error force-undefining global to simulate a browser
+    delete global.process;
+    try {
+      jest.resetModules();
+      const { markMem0OssUsed: browserMark } = await import("../config");
+      await expect(browserMark()).resolves.toBeUndefined();
+    } finally {
+      global.process = originalProcess;
+      jest.resetModules();
+    }
+  });
 });
diff --git a/mem0-ts/src/oss/src/memory/index.ts b/mem0-ts/src/oss/src/memory/index.ts
index f6501945c..05591e615 100644
--- a/mem0-ts/src/oss/src/memory/index.ts
+++ b/mem0-ts/src/oss/src/memory/index.ts
@@ -39,7 +39,7 @@ import {
 } from "./memory.types";
 import { parse_vision_messages } from "../utils/memory";
 import { HistoryManager } from "../storage/base";
-import { captureClientEvent } from "../utils/telemetry";
+import { captureClientEvent, isTelemetryEnabled } from "../utils/telemetry";
 import { lemmatizeForBm25 } from "../utils/lemmatization";
 import {
   extractEntities,
@@ -53,7 +53,7 @@ import {
   ScoredResult,
 } from "../utils/scoring";
 import { getDefaultVectorStoreDbPath } from "../utils/sqlite";
-import { getOrCreateMem0UserId } from "../../../client/config";
+import { getOrCreateMem0UserId, markMem0OssUsed } from "../../../client/config";
 
 // Entity params that must be passed via filters - check both snake_case and camelCase
 const ENTITY_PARAMS = [
@@ -451,6 +451,12 @@ export class Memory {
     try {
       await this._getTelemetryId();
 
+      // Record genuine OSS usage so the platform client may stitch this
+      // machine's anon id to a platform email later.
+      if (isTelemetryEnabled()) {
+        await markMem0OssUsed();
+      }
+
       // Capture initialization event
       await captureClientEvent("init", this, {
         api_version: this.apiVersion,
diff --git a/mem0-ts/src/oss/src/utils/telemetry.ts b/mem0-ts/src/oss/src/utils/telemetry.ts
index 9f75f5d05..2f34416f7 100644
--- a/mem0-ts/src/oss/src/utils/telemetry.ts
+++ b/mem0-ts/src/oss/src/utils/telemetry.ts
@@ -126,4 +126,8 @@ async function captureClientEvent(
   );
 }
 
-export { telemetry, captureClientEvent };
+function isTelemetryEnabled(): boolean {
+  return MEM0_TELEMETRY;
+}
+
+export { telemetry, captureClientEvent, isTelemetryEnabled };
diff --git a/mem0/client/main.py b/mem0/client/main.py
index 01798bd7a..b248b40e3 100644
--- a/mem0/client/main.py
+++ b/mem0/client/main.py
@@ -19,16 +19,13 @@ from mem0.client.types import (
 from mem0.client.utils import api_error_handler
 
 # Exception classes are referenced in docstrings only
-from mem0.memory.setup import get_user_id, is_aliased, mark_aliased, read_anon_ids, setup_config
+from mem0.memory.setup import get_user_id, is_aliased, is_oss_used, mark_aliased, read_anon_ids
 from mem0.memory.telemetry import capture_client_event, client_telemetry
 
 logger = logging.getLogger(__name__)
 
 warnings.filterwarnings("default", category=DeprecationWarning)
 
-# Setup user config
-setup_config()
-
 # Entity parameters that must be passed via filters, not top-level
 ENTITY_PARAMS = frozenset({"user_id", "agent_id", "app_id", "run_id"})
 
@@ -45,6 +42,10 @@ def _validate_and_trim_search_query(query: str) -> str:
 def _maybe_alias_anon_to_email(user_email):
     """Fire $identify per prior anon ID so PostHog merges them into email.
 
+    The OSS user_id is only a stitch candidate when telemetry.oss_used_at
+    proves OSS Memory actually ran here; bare user_id values were historically
+    minted at import time by platform-only clients and must not be stitched.
+    The CLI anon id keeps presence-based stitching (only the CLIs write it).
     Idempotent via telemetry.aliased_pairs: only writes markers when
     telemetry is actually enabled, so disabling/re-enabling MEM0_TELEMETRY still works.
     Best-effort: never raises.
@@ -55,8 +56,9 @@ def _maybe_alias_anon_to_email(user_email):
         return
     try:
         anon_ids = read_anon_ids()
+        oss_id = anon_ids.get("oss") if is_oss_used() else None
         seen = set()
-        for anon_id in (anon_ids.get("oss"), anon_ids.get("cli")):
+        for anon_id in (oss_id, anon_ids.get("cli")):
             if not anon_id or anon_id == user_email or anon_id in seen:
                 continue
             seen.add(anon_id)
diff --git a/mem0/memory/main.py b/mem0/memory/main.py
index 333d2510f..751cc00ae 100644
--- a/mem0/memory/main.py
+++ b/mem0/memory/main.py
@@ -23,7 +23,7 @@ from mem0.configs.prompts import (
 )
 from mem0.exceptions import ValidationError as Mem0ValidationError
 from mem0.memory.base import MemoryBase
-from mem0.memory.setup import mem0_dir, setup_config
+from mem0.memory.setup import mark_oss_used, mem0_dir, setup_config
 from mem0.memory.storage import SQLiteManager
 from mem0.memory.telemetry import MEM0_TELEMETRY, capture_event
 from mem0.memory.utils import (
@@ -341,7 +341,6 @@ def _build_session_scope(filters):
     return "&".join(parts)
 
 
-setup_config()
 logger = logging.getLogger(__name__)
 
 
@@ -410,6 +409,13 @@ class Memory(MemoryBase):
                 self.config.vector_store.provider,
             )
 
+        # Mint the OSS anon id (and record genuine OSS usage) only on real OSS
+        # init, never at import time: platform-only clients must not create
+        # stitch candidates. Must run before the first capture_event so the
+        # telemetry singleton picks up the minted user_id.
+        if MEM0_TELEMETRY:
+            setup_config()
+            mark_oss_used()
         capture_event("mem0.init", self, {"sync_type": "sync"})
 
     @property
@@ -1882,6 +1888,9 @@ class AsyncMemory(MemoryBase):
                 self.config.vector_store.provider,
             )
 
+        if MEM0_TELEMETRY:
+            setup_config()
+            mark_oss_used()
         capture_event("mem0.init", self, {"sync_type": "async"})
 
     @property
diff --git a/mem0/memory/setup.py b/mem0/memory/setup.py
index 7d98bcae4..369fcb036 100644
--- a/mem0/memory/setup.py
+++ b/mem0/memory/setup.py
@@ -2,6 +2,7 @@ import json
 import logging
 import os
 import uuid
+from datetime import datetime, timezone
 from hashlib import sha256
 
 # Set up the directory path
@@ -44,10 +45,12 @@ def _write_config(config):
 def setup_config():
     """Ensure ~/.mem0/config.json exists with a top-level user_id.
 
-    Idempotent: backfills user_id for users whose config was written by the
-    CLI (which writes telemetry.anonymous_id but no top-level user_id).
-    Without this, OSS Python telemetry is silently dropped because
-    get_user_id() returns None when user_id is missing.
+    Called lazily from OSS Memory/AsyncMemory init (never at import time, so
+    platform-only MemoryClient usage mints no anon id). Idempotent: backfills
+    user_id for users whose config was written by the CLI (which writes
+    telemetry.anonymous_id but no top-level user_id). Without this, OSS Python
+    telemetry is silently dropped because get_user_id() returns None when
+    user_id is missing.
     """
     config = _load_config()
     if config.get("user_id"):
@@ -119,6 +122,31 @@ def mark_aliased(anon_id, email):
     _write_config(config)
 
 
+def is_oss_used():
+    """Return whether OSS Memory has genuinely initialized on this machine.
+
+    Gates identity stitching: the top-level user_id is only a stitch candidate
+    when telemetry.oss_used_at is present, because bare user_id values were
+    historically minted at import time by platform-only clients.
+    """
+    config = _load_config()
+    telemetry = config.get("telemetry") if isinstance(config.get("telemetry"), dict) else {}
+    return bool(telemetry.get("oss_used_at"))
+
+
+def mark_oss_used():
+    """Persist telemetry.oss_used_at on first genuine OSS Memory init. Never raises."""
+    config = _load_config()
+    telemetry = config.get("telemetry")
+    if not isinstance(telemetry, dict):
+        telemetry = {}
+    if telemetry.get("oss_used_at"):
+        return
+    telemetry["oss_used_at"] = datetime.now(timezone.utc).isoformat()
+    config["telemetry"] = telemetry
+    _write_config(config)
+
+
 def get_or_create_user_id(vector_store=None):
     """Store user_id in vector store and return it.
 
diff --git a/mem0/memory/telemetry.py b/mem0/memory/telemetry.py
index 0c2c544ad..428f9e694 100644
--- a/mem0/memory/telemetry.py
+++ b/mem0/memory/telemetry.py
@@ -123,7 +123,11 @@ class AnonymousTelemetry:
             self.posthog.capture(
                 distinct_id=email,
                 event="$identify",
-                properties={"$anon_distinct_id": anon_id, "client_source": "python"},
+                properties={
+                    "$anon_distinct_id": anon_id,
+                    "client_source": "python",
+                    "client_version": mem0.__version__,
+                },
             )
             return True
         except Exception as e:
diff --git a/tests/test_telemetry_aliasing.py b/tests/test_telemetry_aliasing.py
index bd6fcf0ee..68e3729f2 100644
--- a/tests/test_telemetry_aliasing.py
+++ b/tests/test_telemetry_aliasing.py
@@ -164,11 +164,68 @@ class TestMarkAliased:
         assert not setup_module.is_aliased("oss-uuid", "other@example.com")
 
 
+# ─── oss_used marker ─────────────────────────────────────────────────────────
+
+
+class TestOssUsedMarker:
+    def test_mark_writes_marker_preserving_fields(self, tmp_mem0_dir):
+        import mem0.memory.setup as setup_module
+
+        _write_config(
+            tmp_mem0_dir,
+            {
+                "user_id": "oss-uuid",
+                "telemetry": {"anonymous_id": "cli-anon", "aliased_pairs": ["pair-marker"]},
+            },
+        )
+        setup_module.mark_oss_used()
+        config = json.loads((tmp_mem0_dir / "config.json").read_text())
+        assert config["user_id"] == "oss-uuid"
+        assert config["telemetry"]["anonymous_id"] == "cli-anon"
+        assert config["telemetry"]["aliased_pairs"] == ["pair-marker"]
+        assert config["telemetry"]["oss_used_at"]
+        assert setup_module.is_oss_used()
+
+    def test_mark_is_idempotent(self, tmp_mem0_dir):
+        import mem0.memory.setup as setup_module
+
+        setup_module.mark_oss_used()
+        first = json.loads((tmp_mem0_dir / "config.json").read_text())["telemetry"]["oss_used_at"]
+        setup_module.mark_oss_used()
+        second = json.loads((tmp_mem0_dir / "config.json").read_text())["telemetry"]["oss_used_at"]
+        assert first == second
+
+    def test_is_oss_used_false_when_no_config(self, tmp_mem0_dir):
+        import mem0.memory.setup as setup_module
+
+        assert not setup_module.is_oss_used()
+
+    def test_is_oss_used_false_without_marker(self, tmp_mem0_dir):
+        import mem0.memory.setup as setup_module
+
+        _write_config(tmp_mem0_dir, {"user_id": "oss-uuid", "telemetry": {"anonymous_id": "cli-anon"}})
+        assert not setup_module.is_oss_used()
+
+    def test_is_oss_used_false_on_malformed_json(self, tmp_mem0_dir):
+        import mem0.memory.setup as setup_module
+
+        (tmp_mem0_dir / "config.json").write_text("{not json")
+        assert not setup_module.is_oss_used()
+
+    def test_mark_does_not_raise_when_config_path_unwritable(self, tmp_mem0_dir):
+        import mem0.memory.setup as setup_module
+
+        (tmp_mem0_dir / "config.json").mkdir()  # open() on a directory fails
+        setup_module.mark_oss_used()  # must not raise
+        assert not setup_module.is_oss_used()
+
+
 # ─── capture_identify ────────────────────────────────────────────────────────
 
 
 class TestCaptureIdentify:
     def test_fires_identify_with_anon_distinct_id(self):
+        import mem0
         import mem0.memory.telemetry as telemetry_module
 
         with patch.object(telemetry_module, "MEM0_TELEMETRY", True):
@@ -181,6 +238,7 @@ class TestCaptureIdentify:
                 assert kwargs["distinct_id"] == "user@example.com"
                 assert kwargs["event"] == "$identify"
                 assert kwargs["properties"]["$anon_distinct_id"] == "anon-123"
+                assert kwargs["properties"]["client_version"] == mem0.__version__
 
     def test_skips_when_anon_equals_email(self):
         import mem0.memory.telemetry as telemetry_module
@@ -230,8 +288,7 @@ class TestCaptureIdentify:
 
 class TestMaybeAliasAnonToEmail:
     """Test the alias helper in isolation by mocking out the config readers
-    and the telemetry client, since module-level setup_config() side effects
-    make end-to-end fixturing awkward."""
+    and the telemetry client, so no real ~/.mem0/config.json is touched."""
 
     def test_fires_identify_for_oss_uuid(self):
         from mem0.client import main as client_main
@@ -242,6 +299,7 @@ class TestMaybeAliasAnonToEmail:
                 "read_anon_ids",
                 return_value={"oss": "oss-uuid", "cli": None, "aliased_pairs": []},
             ),
+            patch.object(client_main, "is_oss_used", return_value=True),
             patch.object(client_main, "is_aliased", return_value=False),
             patch.object(client_main, "mark_aliased") as mark,
             patch.object(client_main, "client_telemetry") as telemetry,
@@ -252,6 +310,7 @@ class TestMaybeAliasAnonToEmail:
             mark.assert_called_once_with("oss-uuid", "user@example.com")
 
     def test_fires_identify_for_cli_anon(self):
+        """The CLI anon id is presence-based: it stitches even without the oss_used marker."""
         from mem0.client import main as client_main
 
         with (
@@ -260,6 +319,7 @@ class TestMaybeAliasAnonToEmail:
                 "read_anon_ids",
                 return_value={"oss": None, "cli": "cli-anon-xyz", "aliased_pairs": []},
             ),
+            patch.object(client_main, "is_oss_used", return_value=False),
             patch.object(client_main, "is_aliased", return_value=False),
             patch.object(client_main, "mark_aliased"),
             patch.object(client_main, "client_telemetry") as telemetry,
@@ -277,6 +337,7 @@ class TestMaybeAliasAnonToEmail:
                 "read_anon_ids",
                 return_value={"oss": "oss-uuid", "cli": "cli-anon", "aliased_pairs": []},
             ),
+            patch.object(client_main, "is_oss_used", return_value=True),
             patch.object(client_main, "is_aliased", return_value=False),
             patch.object(client_main, "mark_aliased"),
             patch.object(client_main, "client_telemetry") as telemetry,
@@ -288,6 +349,26 @@ class TestMaybeAliasAnonToEmail:
             assert ("oss-uuid", "user@example.com") in calls
             assert ("cli-anon", "user@example.com") in calls
 
+    def test_oss_id_requires_oss_used_marker(self):
+        """Without proof of real OSS usage, the oss user_id must never be
+        stitched (it may have been minted by an old platform-only client)."""
+        from mem0.client import main as client_main
+
+        with (
+            patch.object(
+                client_main,
+                "read_anon_ids",
+                return_value={"oss": "oss-uuid", "cli": "cli-anon", "aliased_pairs": []},
+            ),
+            patch.object(client_main, "is_oss_used", return_value=False),
+            patch.object(client_main, "is_aliased", return_value=False),
+            patch.object(client_main, "mark_aliased"),
+            patch.object(client_main, "client_telemetry") as telemetry,
+        ):
+            telemetry.capture_identify.return_value = True
+            client_main._maybe_alias_anon_to_email("user@example.com")
+            telemetry.capture_identify.assert_called_once_with("cli-anon", "user@example.com")
+
     def test_skips_when_pair_already_aliased(self):
         from mem0.client import main as client_main
 
@@ -297,6 +378,7 @@ class TestMaybeAliasAnonToEmail:
                 "read_anon_ids",
                 return_value={"oss": "oss-uuid", "cli": None, "aliased_pairs": ["pair-marker"]},
             ),
+            patch.object(client_main, "is_oss_used", return_value=True),
             patch.object(client_main, "is_aliased", return_value=True),
             patch.object(client_main, "mark_aliased") as mark,
             patch.object(client_main, "client_telemetry") as telemetry,
@@ -342,6 +424,7 @@ class TestMaybeAliasAnonToEmail:
                 "read_anon_ids",
                 return_value={"oss": "oss-uuid", "cli": None, "aliased_pairs": []},
             ),
+            patch.object(client_main, "is_oss_used", return_value=True),
             patch.object(client_main, "is_aliased", return_value=False),
             patch.object(client_main, "mark_aliased") as mark,
             patch.object(client_main, "client_telemetry", mock_telemetry),
@@ -359,6 +442,7 @@ class TestMaybeAliasAnonToEmail:
                 "read_anon_ids",
                 return_value={"oss": "user@example.com", "cli": None, "aliased_pairs": []},
             ),
+            patch.object(client_main, "is_oss_used", return_value=True),
             patch.object(client_main, "is_aliased", return_value=False),
             patch.object(client_main, "mark_aliased"),
             patch.object(client_main, "client_telemetry") as telemetry,
@@ -386,8 +470,12 @@ class TestEndToEndIdempotency:
     calls fire $identify exactly once thanks to the persisted pair marker."""
 
     def test_second_call_is_noop_after_pair_marker_persisted(self, tmp_mem0_dir):
-        # Pre-populate config with an OSS user_id only.
-        _write_config(tmp_mem0_dir, {"user_id": "oss-uuid"})
+        # Pre-populate config with an OSS user_id plus the oss_used_at marker
+        # (without the marker the oss id is no longer a stitch candidate).
+        _write_config(
+            tmp_mem0_dir,
+            {"user_id": "oss-uuid", "telemetry": {"oss_used_at": "2026-01-01T00:00:00+00:00"}},
+        )
         # Reload setup so it uses the tempdir, then reload client.main so it
         # picks up the freshly-loaded read_anon_ids/mark_aliased bindings.
         import mem0.memory.setup as setup_module
@@ -409,3 +497,112 @@ class TestEndToEndIdempotency:
 
         config = json.loads((tmp_mem0_dir / "config.json").read_text())
         assert len(config["telemetry"]["aliased_pairs"]) == 1
+
+    def test_oss_then_platform_stitches_exactly_once(self, tmp_mem0_dir):
+        """Genuine OSS usage (setup_config + mark_oss_used, as Memory.__init__
+        does) followed by platform inits stitches the minted id exactly once."""
+        import mem0.memory.setup as setup_module
+
+        setup_module.setup_config()
+        setup_module.mark_oss_used()
+        oss_id = json.loads((tmp_mem0_dir / "config.json").read_text())["user_id"]
+
+        from mem0.client import main as client_main
+
+        importlib.reload(client_main)
+
+        with patch.object(client_main, "client_telemetry") as telemetry:
+            telemetry.capture_identify.return_value = True
+            client_main._maybe_alias_anon_to_email("user@example.com")
+            telemetry.capture_identify.assert_called_once_with(oss_id, "user@example.com")
+            client_main._maybe_alias_anon_to_email("user@example.com")
+            assert telemetry.capture_identify.call_count == 1
+
+        config = json.loads((tmp_mem0_dir / "config.json").read_text())
+        assert len(config["telemetry"]["aliased_pairs"]) == 1
+        assert config["telemetry"]["oss_used_at"]
+
+
+# ─── Platform-only init must not mint or stitch ──────────────────────────────
+
+
+class TestPlatformOnlyDoesNotMint:
+    """Regression for the bug where importing the client minted an anon id at
+    import time and then stitched it on MemoryClient init, merging an
+    event-less anon person into every platform user."""
+
+    def test_no_config_created_and_no_identify(self, tmp_mem0_dir):
+        from mem0.client import main as client_main
+
+        # Re-execute the client module: it must not create config.json.
+        importlib.reload(client_main)
+        assert not (tmp_mem0_dir / "config.json").exists()
+
+        with patch.object(client_main, "client_telemetry") as telemetry:
+            telemetry.capture_identify.return_value = True
+            client_main._maybe_alias_anon_to_email("user@example.com")
+            telemetry.capture_identify.assert_not_called()
+
+        assert not (tmp_mem0_dir / "config.json").exists()
+
+
+# ─── Lazy minting from OSS Memory init ───────────────────────────────────────
+
+
+class TestLazyOssMinting:
+    """OSS Memory/AsyncMemory init mints the anon id and records genuine OSS
+    usage; nothing happens at import time or with telemetry disabled."""
+
+    def test_memory_init_mints_and_marks(self, tmp_path):
+        import mem0.memory.main as memory_main
+
+        with (
+            patch.object(memory_main, "EmbedderFactory"),
+            patch.object(memory_main, "VectorStoreFactory"),
+            patch.object(memory_main, "LlmFactory"),
+            patch.object(memory_main, "SQLiteManager"),
+            patch.object(memory_main, "capture_event"),
+            patch.object(memory_main, "mem0_dir", str(tmp_path)),
+            patch.object(memory_main, "setup_config") as setup,
+            patch.object(memory_main, "mark_oss_used") as mark,
+            patch.object(memory_main, "MEM0_TELEMETRY", True),
+        ):
+            memory_main.Memory()
+            setup.assert_called_once()
+            mark.assert_called_once()
+
+    def test_memory_init_skips_minting_when_telemetry_disabled(self, tmp_path):
+        import mem0.memory.main as memory_main
+
+        with (
+            patch.object(memory_main, "EmbedderFactory"),
+            patch.object(memory_main, "VectorStoreFactory"),
+            patch.object(memory_main, "LlmFactory"),
+            patch.object(memory_main, "SQLiteManager"),
+            patch.object(memory_main, "capture_event"),
+            patch.object(memory_main, "mem0_dir", str(tmp_path)),
+            patch.object(memory_main, "setup_config") as setup,
+            patch.object(memory_main, "mark_oss_used") as mark,
+            patch.object(memory_main, "MEM0_TELEMETRY", False),
+        ):
+            memory_main.Memory()
+            setup.assert_not_called()
+            mark.assert_not_called()
+
+    def test_async_memory_init_mints_and_marks(self, tmp_path):
+        import mem0.memory.main as memory_main
+
+        with (
+            patch.object(memory_main, "EmbedderFactory"),
+            patch.object(memory_main, "VectorStoreFactory"),
+            patch.object(memory_main, "LlmFactory"),
+            patch.object(memory_main, "SQLiteManager"),
+            patch.object(memory_main, "capture_event"),
+            patch.object(memory_main, "mem0_dir", str(tmp_path)),
+            patch.object(memory_main, "setup_config") as setup,
+            patch.object(memory_main, "mark_oss_used") as mark,
+            patch.object(memory_main, "MEM0_TELEMETRY", True),
+        ):
+            memory_main.AsyncMemory()
+            setup.assert_called_once()
+            mark.assert_called_once()