diff --git a/tests/test_litellm/proxy/agent_session_endpoints/test_ownership.py b/tests/test_litellm/proxy/agent_session_endpoints/test_ownership.py
new file mode 100644
index 00000000000..ab31ae51577
--- /dev/null
+++ b/tests/test_litellm/proxy/agent_session_endpoints/test_ownership.py
@@ -0,0 +1,93 @@
+"""
+Validation #10 — cross-tenant isolation at all 3 levels.
+
+Tenant A creates an agent + session + run. Tenant B (different api_key)
+must get 404 on every read/write of those resources.
+"""
+
+
+def test_cross_tenant_isolation(client, other_tenant_client, noop_provider):
+    # Tenant A creates an agent + session + run.
+    agent = client.post(
+        "/v2/agents",
+        headers={"Authorization": "Bearer k"},
+        json={"name": "secret", "model": "gpt-4"},
+    ).json()
+    aid = agent["id"]
+    sess = client.post(
+        "/v2/sessions",
+        headers={"Authorization": "Bearer k"},
+        json={"agent_id": aid, "repos": []},
+    ).json()
+    sid = sess["id"]
+    run = client.post(
+        f"/v2/sessions/{sid}/runs",
+        headers={"Authorization": "Bearer k"},
+        json={"prompt": {"text": "x"}},
+    ).json()
+    rid = run["id"]
+
+    # Tenant B sees nothing.
+    assert (
+        other_tenant_client.get(
+            f"/v2/agents/{aid}", headers={"Authorization": "Bearer other"}
+        ).status_code
+        == 404
+    )
+    assert (
+        other_tenant_client.get(
+            f"/v2/sessions/{sid}", headers={"Authorization": "Bearer other"}
+        ).status_code
+        == 404
+    )
+    assert (
+        other_tenant_client.get(
+            f"/v2/sessions/{sid}/runs/{rid}",
+            headers={"Authorization": "Bearer other"},
+        ).status_code
+        == 404
+    )
+
+    # Tenant B's list endpoints return only their own (none).
+    assert (
+        other_tenant_client.get(
+            "/v2/agents", headers={"Authorization": "Bearer other"}
+        ).json()["data"]
+        == []
+    )
+    assert (
+        other_tenant_client.get(
+            "/v2/sessions", headers={"Authorization": "Bearer other"}
+        ).json()["data"]
+        == []
+    )
+
+    # Tenant B can't delete tenant A's agent/session.
+    assert (
+        other_tenant_client.delete(
+            f"/v2/agents/{aid}", headers={"Authorization": "Bearer other"}
+        ).status_code
+        == 404
+    )
+    assert (
+        other_tenant_client.delete(
+            f"/v2/sessions/{sid}", headers={"Authorization": "Bearer other"}
+        ).status_code
+        == 404
+    )
+
+
+def test_admin_sees_all_tenants(client, admin_client, noop_provider):
+    """Proxy admin can read across tenants — admins exist for support
+    and ops and bypassing the owner filter is intentional."""
+    agent = client.post(
+        "/v2/agents",
+        headers={"Authorization": "Bearer k"},
+        json={"name": "tenant-A", "model": "gpt-4"},
+    ).json()
+
+    # Admin can fetch tenant A's agent.
+    res = admin_client.get(
+        f"/v2/agents/{agent['id']}", headers={"Authorization": "Bearer admin"}
+    )
+    assert res.status_code == 200