diff --git a/tests/test_litellm/proxy/agent_session_endpoints/test_agent_reuse.py b/tests/test_litellm/proxy/agent_session_endpoints/test_agent_reuse.py
new file mode 100644
index 00000000000..50ee3c9cdac
--- /dev/null
+++ b/tests/test_litellm/proxy/agent_session_endpoints/test_agent_reuse.py
@@ -0,0 +1,57 @@
+"""
+Validation #3 — one agent, multiple sessions; agent_id is stable across
+sessions.
+"""
+
+
+def _create_agent(client) -> str:
+    res = client.post(
+        "/v2/agents",
+        headers={"Authorization": "Bearer k"},
+        json={"name": "test", "model": "gpt-4"},
+    )
+    assert res.status_code == 200, res.text
+    return res.json()["id"]
+
+
+def _create_session(client, agent_id: str) -> str:
+    res = client.post(
+        "/v2/sessions",
+        headers={"Authorization": "Bearer k"},
+        json={"agent_id": agent_id, "repos": []},
+    )
+    assert res.status_code == 200, res.text
+    return res.json()["id"]
+
+
+def test_agent_reused_across_three_sessions(client, noop_provider):
+    agent_id = _create_agent(client)
+
+    session_ids = [_create_session(client, agent_id) for _ in range(3)]
+
+    # Sessions are distinct IDs but all reference the same agent_id.
+    assert len(set(session_ids)) == 3
+    for sid in session_ids:
+        get_res = client.get(
+            f"/v2/sessions/{sid}", headers={"Authorization": "Bearer k"}
+        )
+        assert get_res.status_code == 200
+        assert get_res.json()["agent_id"] == agent_id
+
+
+def test_agent_id_format(client, noop_provider):
+    agent_id = _create_agent(client)
+    assert agent_id.startswith("agent_")
+
+
+def test_sessions_under_agent_listed_by_filter(client, noop_provider):
+    agent_id = _create_agent(client)
+    sids = [_create_session(client, agent_id) for _ in range(2)]
+
+    res = client.get(
+        f"/v2/sessions?agent_id={agent_id}",
+        headers={"Authorization": "Bearer k"},
+    )
+    assert res.status_code == 200
+    listed_ids = {s["id"] for s in res.json()["data"]}
+    assert listed_ids == set(sids)