diff --git a/.sampo/changesets/mcp-interface-server-events.md b/.sampo/changesets/mcp-interface-server-events.md
new file mode 100644
index 000000000..d057795ba
--- /dev/null
+++ b/.sampo/changesets/mcp-interface-server-events.md
@@ -0,0 +1,5 @@
+---
+pypi/posthog: patch
+---
+
+Set `$mcp_interface` to `mcp` on events from MCP servers.
diff --git a/posthog/mcp/_posthog_events.py b/posthog/mcp/_posthog_events.py
index 90040011a..7113bd2cb 100644
--- a/posthog/mcp/_posthog_events.py
+++ b/posthog/mcp/_posthog_events.py
@@ -59,7 +59,10 @@ def build_posthog_capture_events(
 
 
 def _build_capture_event(event: Event) -> PostHogCaptureEvent:
-    properties: Dict[str, Any] = {_P.SOURCE: POSTHOG_MCP_ANALYTICS_SOURCE}
+    properties: Dict[str, Any] = {
+        _P.INTERFACE: "mcp",
+        _P.SOURCE: POSTHOG_MCP_ANALYTICS_SOURCE,
+    }
     _add_session_id(event, properties)
     _add_conversation_id(event, properties)
     _add_person_processing(event, properties)
@@ -260,7 +263,7 @@ def _add_server_build(event: Event, properties: Dict[str, Any]) -> None:
 
 
 def _build_exception_event(event: Event) -> PostHogCaptureEvent:
-    properties: Dict[str, Any] = {}
+    properties: Dict[str, Any] = {_P.INTERFACE: "mcp"}
     _add_session_id(event, properties)
     _add_conversation_id(event, properties)
     _add_person_processing(event, properties)
diff --git a/posthog/mcp/constants.py b/posthog/mcp/constants.py
index ee8cf96ae..ab5dd363e 100644
--- a/posthog/mcp/constants.py
+++ b/posthog/mcp/constants.py
@@ -84,6 +84,7 @@ class PostHogMCPAnalyticsProperty:
     FEEDBACK_TASK_COMPLETED = "$mcp_feedback_task_completed"
     FEEDBACK_TOOL = "$mcp_feedback_tool"
     FEEDBACK_TYPE = "$mcp_feedback_type"
+    INTERFACE = "$mcp_interface"
     IS_ERROR = "$mcp_is_error"
     INTENT = "$mcp_intent"
     INTENT_SOURCE = "$mcp_intent_source"
diff --git a/posthog/test/mcp/test_pipeline.py b/posthog/test/mcp/test_pipeline.py
index 81b6db644..c3e39f2cf 100644
--- a/posthog/test/mcp/test_pipeline.py
+++ b/posthog/test/mcp/test_pipeline.py
@@ -885,6 +885,7 @@ def test_build_tool_call_event_properties():
     props = capture["properties"]
     assert capture["event"] == PostHogMCPAnalyticsEvent.TOOL_CALL
     assert capture["distinct_id"] == "ses_abc"
+    assert props[PostHogMCPAnalyticsProperty.INTERFACE] == "mcp"
     assert props[PostHogMCPAnalyticsProperty.SOURCE] == POSTHOG_MCP_ANALYTICS_SOURCE
     assert props[PostHogMCPAnalyticsProperty.TOOL_NAME] == "search_events"
     assert props[PostHogMCPAnalyticsProperty.TOOL_CATEGORY] == "Logs"
@@ -912,6 +913,7 @@ def test_protocol_version_on_primary_and_exception_events():
     # Both the primary $mcp_tool_call and the $exception sibling carry it.
     assert len(captures) == 2
     for capture in captures:
+        assert capture["properties"][PostHogMCPAnalyticsProperty.INTERFACE] == "mcp"
         assert (
             capture["properties"][PostHogMCPAnalyticsProperty.PROTOCOL_VERSION]
             == "2025-06-18"
diff --git a/references/public_api_snapshot.txt b/references/public_api_snapshot.txt
index 51ee00d9d..3e2926e5a 100644
--- a/references/public_api_snapshot.txt
+++ b/references/public_api_snapshot.txt
@@ -909,6 +909,7 @@ attribute posthog.mcp.constants.PostHogMCPAnalyticsProperty.INPUT_ALIASES_USED =
 attribute posthog.mcp.constants.PostHogMCPAnalyticsProperty.INPUT_KEYS = '$mcp_input_keys'
 attribute posthog.mcp.constants.PostHogMCPAnalyticsProperty.INTENT = '$mcp_intent'
 attribute posthog.mcp.constants.PostHogMCPAnalyticsProperty.INTENT_SOURCE = '$mcp_intent_source'
+attribute posthog.mcp.constants.PostHogMCPAnalyticsProperty.INTERFACE = '$mcp_interface'
 attribute posthog.mcp.constants.PostHogMCPAnalyticsProperty.IS_ERROR = '$mcp_is_error'
 attribute posthog.mcp.constants.PostHogMCPAnalyticsProperty.LISTED_TOOL_NAMES = '$mcp_listed_tool_names'
 attribute posthog.mcp.constants.PostHogMCPAnalyticsProperty.LLM_MODEL = '$mcp_llm_model'