diff --git a/src/software/gameplay_tests/simulated_test_fixture.py b/src/software/gameplay_tests/simulated_test_fixture.py
index 71c14e1c85..3b7c26213b 100644
--- a/src/software/gameplay_tests/simulated_test_fixture.py
+++ b/src/software/gameplay_tests/simulated_test_fixture.py
@@ -591,7 +591,8 @@ def simulated_test_runner():
         running_in_realtime=args.enable_thunderscope and not args.ci_mode,
     ) as yellow_fs:
         with Gamecontroller(
-            suppress_logs=(not args.show_gamecontroller_logs)
+            suppress_logs=(not args.show_gamecontroller_logs),
+            parallelized=True,
         ) as gamecontroller:
             blue_fs.setup_proto_unix_io(blue_full_system_proto_unix_io)
             yellow_fs.setup_proto_unix_io(yellow_full_system_proto_unix_io)
diff --git a/src/software/thunderscope/binary_context_managers/BUILD b/src/software/thunderscope/binary_context_managers/BUILD
index 0fe462dd43..1d363161ce 100644
--- a/src/software/thunderscope/binary_context_managers/BUILD
+++ b/src/software/thunderscope/binary_context_managers/BUILD
@@ -24,6 +24,7 @@ py_library(
         "//software/networking:ssl_proto_communication",
         "//software/thunderscope:util",
         "//software/thunderscope/common:thread_safe_circular_buffer",
+        requirement("netifaces"),
     ],
 )
 
diff --git a/src/software/thunderscope/binary_context_managers/game_controller.py b/src/software/thunderscope/binary_context_managers/game_controller.py
index 99555b0758..f4150067d6 100644
--- a/src/software/thunderscope/binary_context_managers/game_controller.py
+++ b/src/software/thunderscope/binary_context_managers/game_controller.py
@@ -7,6 +7,8 @@
 import logging
 import os
 import time
+import netifaces
+
 from subprocess import Popen
 from typing import Any
 
@@ -44,15 +46,18 @@ def __init__(
         suppress_logs: bool = False,
         use_conventional_port: bool = False,
         automate_referee: bool = False,
+        parallelized: bool = False,
     ) -> None:
         """Run Gamecontroller
 
         :param suppress_logs: True if logs should be suppressed
         :param use_conventional_port: True when using static referee port. False for dynamic port assignments.
-        :param automate_referee: True if referee commands should be automated
+        :param automate_referee: True if referee commands should be automated.
+        :param parallelized: True when this is one of many Gamecontrollers running at once.
         """
         self.suppress_logs = suppress_logs
         self.automate_referee = automate_referee
+        self.parallelized = parallelized
 
         self.use_conventional_port = use_conventional_port
         self.referee_port = None
@@ -109,17 +114,20 @@ def __enter__(self) -> Gamecontroller:
 
             command += ["-publishAddress", f"{self.REFEREE_IP}:{self.referee_port}"]
             command += ["-ciAddress", f"localhost:{self.ci_port}"]
-            command += [
-                "-address",
-                "localhost:0",
-                "-autorefAddress",
-                "localhost:0",
-                "-remoteControlAddress",
-                "localhost:0",
-                "-teamAddress",
-                "localhost:0",
-                "-backendOnly",
-            ]
+            if self.parallelized:
+                # One of many GCs running at once: no web UI and all-dynamic ports so
+                # instances don't collide on the fixed UI / autoref ports.
+                command += [
+                    "-address",
+                    "localhost:0",
+                    "-autorefAddress",
+                    "localhost:0",
+                    "-remoteControlAddress",
+                    "localhost:0",
+                    "-teamAddress",
+                    "localhost:0",
+                    "-backendOnly",
+                ]
 
             if self.suppress_logs:
                 with open(os.devnull, "w") as fp:
@@ -245,15 +253,10 @@ def __send_referee_command(data: Referee) -> None:
             if autoref_proto_unix_io is not None:
                 autoref_proto_unix_io.send_proto(Referee, data)
 
-        if is_current_platform_macos():
-            loopback_iface = "en0"
-        else:
-            loopback_iface = "lo"
-
         self.receive_referee_command = tbots_cpp.SSLRefereeProtoListener(
             Gamecontroller.REFEREE_IP,
             self.referee_port,
-            loopback_iface,
+            self.__get_referee_multicast_interface(),
             __send_referee_command,
             True,
         )
@@ -630,3 +633,19 @@ def __update_robot_count(
                 robot_states[removed_robot_ids.get_nowait()].CopyFrom(place_state)
             except queue.Empty:
                 return
+
+    @staticmethod
+    def __get_referee_multicast_interface() -> str:
+        """Determine the network interface to join the referee multicast group on.
+
+        :return: the name of the interface to receive referee multicast on
+        """
+        if not is_current_platform_macos():
+            return "lo"
+
+        default = netifaces.gateways().get("default", {}).get(netifaces.AF_INET)
+        if default:
+            # default is a (gateway_ip, interface_name) tuple
+            return default[1]
+
+        raise RuntimeError("Could not determine the default network interface on macOS")