diff --git a/hermes_cli/banner.py b/hermes_cli/banner.py
index a581ba15f..c91b2f728 100644
--- a/hermes_cli/banner.py
+++ b/hermes_cli/banner.py
@@ -221,7 +221,11 @@ def check_for_updates() -> Optional[int]:
     cache_file = hermes_home / ".update_check"
     embedded_rev = os.environ.get("HERMES_REVISION") or None
 
-    # Read cache — invalidate if the embedded rev has changed since last check
+    # Read cache — invalidate if the embedded rev OR installed version has
+    # changed since the last check. The version guard matters for pip installs:
+    # `check_via_pypi()` compares against VERSION, so a `pip install --upgrade`
+    # changes VERSION but leaves rev unchanged (both None), and without this
+    # the stale "behind" count would survive the upgrade for up to 6h. See #34491.
     now = time.time()
     try:
         if cache_file.exists():
@@ -229,6 +233,7 @@ def check_for_updates() -> Optional[int]:
             if (
                 now - cached.get("ts", 0) < _UPDATE_CHECK_CACHE_SECONDS
                 and cached.get("rev") == embedded_rev
+                and cached.get("ver") == VERSION
             ):
                 return cached.get("behind")
     except Exception:
@@ -249,7 +254,9 @@ def check_for_updates() -> Optional[int]:
             behind = _check_via_local_git(repo_dir)
 
     try:
-        cache_file.write_text(json.dumps({"ts": now, "behind": behind, "rev": embedded_rev}))
+        cache_file.write_text(
+            json.dumps({"ts": now, "behind": behind, "rev": embedded_rev, "ver": VERSION})
+        )
     except Exception:
         pass
 
@@ -691,6 +698,21 @@ def build_welcome_banner(console: Console, model: str, cwd: str,
     except Exception:
         pass  # Never break the banner over an update check
 
+    # Pip-install warning — `pip install hermes-agent` is not the supported
+    # install path (it exists on PyPI for internal/CI reasons, not end users).
+    # Such installs miss the git checkout + installer-managed deps, so updates,
+    # self-update, and issue triage don't behave correctly. Warn, don't block.
+    try:
+        from hermes_cli.config import detect_install_method
+        if detect_install_method() == "pip":
+            right_lines.append(
+                "[bold yellow]⚠ pip install not officially supported[/]"
+                "[dim yellow] — exists for reasons other than user install; "
+                "expect instability and an inability to support issues[/]"
+            )
+    except Exception:
+        pass  # Never break the banner over the install-method check
+
     right_content = "\n".join(right_lines)
     layout_table.add_row(left_content, right_content)
 
diff --git a/tests/hermes_cli/test_pip_install_detection.py b/tests/hermes_cli/test_pip_install_detection.py
index bfdc8be4f..49df74f62 100644
--- a/tests/hermes_cli/test_pip_install_detection.py
+++ b/tests/hermes_cli/test_pip_install_detection.py
@@ -59,3 +59,53 @@ def test_docker_detected_via_dockerenv(tmp_path):
 def test_recommended_update_command_docker():
     from hermes_cli.config import recommended_update_command_for_method
     assert "docker pull" in recommended_update_command_for_method("docker")
+
+
+def test_banner_warns_on_pip_install(tmp_path):
+    """The welcome banner surfaces a warning when the install method is pip."""
+    import io
+    from rich.console import Console
+    from hermes_cli import banner
+
+    hh = tmp_path / ".hermes"
+    hh.mkdir()
+    (hh / ".install_method").write_text("pip\n")
+
+    with patch("hermes_cli.config.get_hermes_home", return_value=hh), \
+         patch("hermes_constants.get_hermes_home", return_value=hh):
+        buf = io.StringIO()
+        # Wide console so the warning isn't wrapped across lines in the panel.
+        console = Console(file=buf, width=400, force_terminal=False, color_system=None)
+        banner.build_welcome_banner(
+            console, model="m", cwd="/tmp",
+            tools=[{"function": {"name": "terminal"}}],
+            enabled_toolsets=["terminal"],
+        )
+        out = buf.getvalue()
+
+    assert "officially" in out
+    assert "instability" in out
+
+
+def test_banner_no_pip_warning_on_git_install(tmp_path):
+    """Git installs must not show the pip-install warning."""
+    import io
+    from rich.console import Console
+    from hermes_cli import banner
+
+    hh = tmp_path / ".hermes"
+    hh.mkdir()
+    (hh / ".install_method").write_text("git\n")
+
+    with patch("hermes_cli.config.get_hermes_home", return_value=hh), \
+         patch("hermes_constants.get_hermes_home", return_value=hh):
+        buf = io.StringIO()
+        console = Console(file=buf, width=400, force_terminal=False, color_system=None)
+        banner.build_welcome_banner(
+            console, model="m", cwd="/tmp",
+            tools=[{"function": {"name": "terminal"}}],
+            enabled_toolsets=["terminal"],
+        )
+        out = buf.getvalue()
+
+    assert "officially" not in out
diff --git a/tests/hermes_cli/test_update_check.py b/tests/hermes_cli/test_update_check.py
index 8a68d6a17..c7cc1c867 100644
--- a/tests/hermes_cli/test_update_check.py
+++ b/tests/hermes_cli/test_update_check.py
@@ -19,6 +19,7 @@ def test_version_string_no_v_prefix():
 def test_check_for_updates_uses_cache(tmp_path, monkeypatch):
     """When cache is fresh, check_for_updates should return cached value without calling git."""
     from hermes_cli.banner import check_for_updates
+    from hermes_cli import __version__
 
     # Create a fake git repo and fresh cache
     repo_dir = tmp_path / "hermes-agent"
@@ -26,7 +27,7 @@ def test_check_for_updates_uses_cache(tmp_path, monkeypatch):
     (repo_dir / ".git").mkdir()
 
     cache_file = tmp_path / ".update_check"
-    cache_file.write_text(json.dumps({"ts": time.time(), "behind": 3}))
+    cache_file.write_text(json.dumps({"ts": time.time(), "behind": 3, "ver": __version__}))
 
     monkeypatch.setenv("HERMES_HOME", str(tmp_path))
     with patch("hermes_cli.banner.subprocess.run") as mock_run:
@@ -36,6 +37,43 @@ def test_check_for_updates_uses_cache(tmp_path, monkeypatch):
     mock_run.assert_not_called()
 
 
+def test_check_for_updates_invalidates_on_version_change(tmp_path, monkeypatch):
+    """A fresh cache from a different installed version must be re-checked, not reused.
+
+    Regression for #34491: after `pip install --upgrade`, VERSION changes but the
+    cache's 6h TTL hadn't expired and rev was unchanged (both None), so the stale
+    'behind' count survived the upgrade. The version guard forces a recheck.
+    """
+    import hermes_cli.banner as banner
+
+    # No local git checkout -> the PyPI path is exercised (pip-install class).
+    fake_banner = tmp_path / "hermes_cli" / "banner.py"
+    fake_banner.parent.mkdir(parents=True, exist_ok=True)
+    fake_banner.touch()
+    monkeypatch.setattr(banner, "__file__", str(fake_banner))
+
+    # Fresh (within TTL) cache that says "behind", but stamped with an OLD version.
+    cache_file = tmp_path / ".update_check"
+    cache_file.write_text(
+        json.dumps({"ts": time.time(), "behind": 1, "rev": None, "ver": "0.0.1-old"})
+    )
+
+    monkeypatch.setenv("HERMES_HOME", str(tmp_path))
+    monkeypatch.delenv("HERMES_REVISION", raising=False)
+    with patch("hermes_cli.banner.subprocess.run") as mock_run, \
+         patch("hermes_cli.banner.check_via_pypi", return_value=0) as mock_pypi:
+        result = banner.check_for_updates()
+
+    # Stale-version cache rejected -> fresh check ran -> up-to-date result.
+    assert result == 0
+    mock_pypi.assert_called_once()
+    mock_run.assert_not_called()
+
+    # Cache rewritten with the current installed version.
+    written = json.loads(cache_file.read_text())
+    assert written["ver"] == banner.VERSION
+
+
 def test_check_for_updates_expired_cache(tmp_path, monkeypatch):
     """When cache is expired, check_for_updates should call git fetch."""
     from hermes_cli.banner import check_for_updates