diff --git a/mempalace/llm_client.py b/mempalace/llm_client.py
index 837247b5a..9d6514239 100644
--- a/mempalace/llm_client.py
+++ b/mempalace/llm_client.py
@@ -49,6 +49,8 @@ def _endpoint_is_local(url: Optional[str]) -> bool:
       - localhost, 127.0.0.1, ::1
       - hostnames ending in .local (mDNS/Bonjour)
       - IPv4 RFC1918: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16
+      - IPv4 CGNAT (Tailscale and similar VPN/tunnel networks):
+        100.64.0.0/10 — first octet 100, second octet 64-127 inclusive
       - IPv6 unique-local addresses (fc00::/7) — fc.../fd... prefixes
 
     None / empty / unparseable URLs are treated as local (defensive default —
@@ -81,6 +83,20 @@ def _endpoint_is_local(url: Optional[str]) -> bool:
                     return True
             except ValueError:
                 pass
+    if host.startswith("100."):
+        # 100.64.0.0/10 — Tailscale CGNAT range. First octet 100, second
+        # octet 64-127 inclusive. Users running a local LLM (LM Studio,
+        # Ollama, etc.) accessible via Tailscale on a 100.x.x.x address
+        # should not trigger the external-API privacy warning.
+        # 100.x.x.x outside this range is regular allocated public space
+        # and remains external.
+        parts = host.split(".")
+        if len(parts) >= 2:
+            try:
+                if 64 <= int(parts[1]) <= 127:
+                    return True
+            except ValueError:
+                pass
     # IPv6 unique-local addresses fc00::/7 — match leading hex chars
     if host.startswith("fc") or host.startswith("fd"):
         return True
diff --git a/tests/test_llm_client.py b/tests/test_llm_client.py
index d9dd6e9b1..f5259941f 100644
--- a/tests/test_llm_client.py
+++ b/tests/test_llm_client.py
@@ -378,3 +378,51 @@ def test_anthropic_provider_default_endpoint_is_external():
         f"Default AnthropicProvider endpoint must be external; got "
         f"is_external_service={p.is_external_service} for endpoint={p.endpoint}"
     )
+
+
+# ── Tailscale CGNAT range (issue #25 follow-up to #24) ──────────────────
+#
+# Tailscale assigns addresses in 100.64.0.0/10 (CGNAT range): first octet
+# always 100, second octet 64-127 inclusive. Users running LM Studio /
+# Ollama / any local LLM accessible via Tailscale would currently
+# (post-#24, pre-#25) get a wrong privacy warning because the heuristic
+# doesn't recognize CGNAT as private. These tests pin the fix.
+
+
+def test_openai_compat_provider_tailscale_cgnat_endpoint_is_local():
+    """Tailscale CGNAT range (100.64.0.0/10) — IPs where the first octet
+    is 100 AND the second octet is 64-127 inclusive — must be classified
+    as local. Tailscale users running LM Studio on their Tailnet should
+    not trigger the external-API warning.
+    """
+    cases = [
+        ("http://100.64.0.1:1234", "start of CGNAT"),
+        ("http://100.100.50.50:1234", "middle of CGNAT (typical Tailscale assignment)"),
+        ("http://100.127.255.254:1234", "near end of CGNAT"),
+    ]
+    for endpoint, label in cases:
+        p = OpenAICompatProvider(model="any", endpoint=endpoint)
+        assert p.is_external_service is False, (
+            f"Tailscale CGNAT address {endpoint} ({label}) must be classified "
+            f"local; got is_external_service={p.is_external_service}"
+        )
+
+
+def test_openai_compat_provider_outside_tailscale_cgnat_is_external():
+    """Addresses in 100.x.x.x that fall OUTSIDE the CGNAT range
+    (100.64.0.0 - 100.127.255.255) are public IPs in regular allocated
+    space and must remain classified as external. Specifically: anything
+    where the second octet is < 64 or > 127.
+    """
+    cases = [
+        ("http://100.0.0.1:1234", "below CGNAT (public)"),
+        ("http://100.63.255.255:1234", "just below CGNAT (boundary)"),
+        ("http://100.128.0.0:1234", "just above CGNAT (boundary)"),
+        ("http://100.255.255.255:1234", "well above CGNAT"),
+    ]
+    for endpoint, label in cases:
+        p = OpenAICompatProvider(model="any", endpoint=endpoint)
+        assert p.is_external_service is True, (
+            f"Address {endpoint} ({label}) is OUTSIDE Tailscale CGNAT and "
+            f"should remain external; got is_external_service={p.is_external_service}"
+        )