diff --git a/frontend/src/lib/taxonomy.tsx b/frontend/src/lib/taxonomy.tsx
index e1ec166e123c2..ac540c67f49a1 100644
--- a/frontend/src/lib/taxonomy.tsx
+++ b/frontend/src/lib/taxonomy.tsx
@@ -672,6 +672,11 @@ export const CORE_FILTER_DEFINITIONS_BY_GROUP = {
             description: 'What library was used to send the event.',
             examples: ['web', 'posthog-ios'],
         },
+        $lib_custom_api_host: {
+            label: 'Library Custom API Host',
+            description: 'The custom API host used to send the event.',
+            examples: ['https://ph.example.com'],
+        },
         $lib_version: {
             label: 'Library Version',
             description: 'Version of the library used to send the event. Used in combination with Library.',
diff --git a/posthog/api/property_definition.py b/posthog/api/property_definition.py
index 9ffa473189243..7c026e4e634d4 100644
--- a/posthog/api/property_definition.py
+++ b/posthog/api/property_definition.py
@@ -313,6 +313,7 @@ def _join_on_event_property(self):
     "$group_4": "Group 5",
     "$ip": "IP Address",
     "$lib": "Library",
+    "$lib_custom_api_host": "Library Custom API Host",
     "$lib_version": "Library Version",
     "$lib_version__major": "Library Version (Major)",
     "$lib_version__minor": "Library Version (Minor)",