diff --git a/infra/specs/client.webrtc.json b/infra/specs/client.webrtc.json
index 64c5585833..c00cd1cdc3 100644
--- a/infra/specs/client.webrtc.json
+++ b/infra/specs/client.webrtc.json
@@ -9212,7 +9212,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 2
         },
         "test_id_prefix": "ninja://modules:modules_tests/"
       },
@@ -9261,7 +9262,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 6
         },
         "test_id_prefix": "ninja://modules:modules_unittests/"
       },
@@ -9457,7 +9459,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 6
         },
         "test_id_prefix": "ninja://:rtc_unittests/"
       },
@@ -9802,7 +9805,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 4
         },
         "test_id_prefix": "ninja://:video_engine_tests/"
       },
@@ -10199,7 +10203,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 2
         },
         "test_id_prefix": "ninja://modules:modules_tests/"
       },
@@ -10248,7 +10253,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 6
         },
         "test_id_prefix": "ninja://modules:modules_unittests/"
       },
@@ -10444,7 +10450,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 6
         },
         "test_id_prefix": "ninja://:rtc_unittests/"
       },
@@ -10789,7 +10796,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 4
         },
         "test_id_prefix": "ninja://:video_engine_tests/"
       },
@@ -11186,7 +11194,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 2
         },
         "test_id_prefix": "ninja://modules:modules_tests/"
       },
@@ -11235,7 +11244,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 6
         },
         "test_id_prefix": "ninja://modules:modules_unittests/"
       },
@@ -11431,7 +11441,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 6
         },
         "test_id_prefix": "ninja://:rtc_unittests/"
       },
@@ -11776,7 +11787,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 4
         },
         "test_id_prefix": "ninja://:video_engine_tests/"
       },
diff --git a/infra/specs/internal.client.webrtc.json b/infra/specs/internal.client.webrtc.json
index 7ef9550fd5..a4e8d9a322 100644
--- a/infra/specs/internal.client.webrtc.json
+++ b/infra/specs/internal.client.webrtc.json
@@ -134,7 +134,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 2
         },
         "test_id_prefix": "ninja://modules:modules_tests/"
       },
@@ -178,7 +179,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 6
         },
         "test_id_prefix": "ninja://modules:modules_unittests/"
       },
@@ -486,7 +488,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 4
         },
         "test_id_prefix": "ninja://:video_engine_tests/"
       }
@@ -681,7 +684,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 2
         },
         "test_id_prefix": "ninja://modules:modules_tests/"
       },
@@ -725,7 +729,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 6
         },
         "test_id_prefix": "ninja://modules:modules_unittests/"
       },
@@ -1033,7 +1038,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 4
         },
         "test_id_prefix": "ninja://:video_engine_tests/"
       }
diff --git a/infra/specs/mixins.pyl b/infra/specs/mixins.pyl
index 525688c08a..9459e9f813 100644
--- a/infra/specs/mixins.pyl
+++ b/infra/specs/mixins.pyl
@@ -268,6 +268,21 @@
       }
     }
   },
+  'shards-2': {
+    'swarming': {
+      'shards': 2
+    }
+  },
+  'shards-4': {
+    'swarming': {
+      'shards': 4
+    }
+  },
+  'shards-6': {
+    'swarming': {
+      'shards': 6
+    }
+  },
   'timeout-2h': {
     'swarming': {
       'hard_timeout': 7200,
diff --git a/infra/specs/mixins_webrtc.pyl b/infra/specs/mixins_webrtc.pyl
index 287c69c659..43d9c8b9a0 100644
--- a/infra/specs/mixins_webrtc.pyl
+++ b/infra/specs/mixins_webrtc.pyl
@@ -203,6 +203,21 @@
       'result_format': 'json'
     }
   },
+  'shards-2': {
+    'swarming': {
+      'shards': 2,
+    },
+  },
+  'shards-4': {
+    'swarming': {
+      'shards': 4,
+    },
+  },
+  'shards-6': {
+    'swarming': {
+      'shards': 6,
+    },
+  },
   'shamu': {
     'swarming': {
       'dimensions': {
diff --git a/infra/specs/test_suites.pyl b/infra/specs/test_suites.pyl
index 92de58d12e..386d5ceeeb 100644
--- a/infra/specs/test_suites.pyl
+++ b/infra/specs/test_suites.pyl
@@ -35,36 +35,26 @@
       'common_video_unittests': {},
       'dcsctp_unittests': {},
       'modules_tests': {
-        'swarming': {
-          'shards': 2
-        },
+        'mixins': ['shards-2'],
       },
       'modules_unittests': {
-        'swarming': {
-          'shards': 6
-        },
+        'mixins': ['shards-6'],
       },
       'peerconnection_unittests': {
-        'swarming': {
-          'shards': 4
-        },
+        'mixins': ['shards-4'],
       },
       'rtc_media_unittests': {},
       'rtc_pc_unittests': {},
       'rtc_stats_unittests': {},
       'rtc_unittests': {
-        'swarming': {
-          'shards': 6
-        },
+        'mixins': ['shards-6'],
       },
       'slow_peer_connection_unittests': {},
       'system_wrappers_unittests': {},
       'test_support_unittests': {},
       'tools_unittests': {},
       'video_engine_tests': {
-        'swarming': {
-          'shards': 4
-        },
+        'mixins': ['shards-4'],
       },
       'voip_unittests': {},
       'webrtc_nonparallel_tests': {},
@@ -96,36 +86,26 @@
         'args': ['--quick']
       },
       'modules_tests': {
-        'swarming': {
-          'shards': 2
-        },
+        'mixins': ['shards-2'],
       },
       'modules_unittests': {
-        'swarming': {
-          'shards': 6
-        },
+        'mixins': ['shards-6'],
       },
       'peerconnection_unittests': {
-        'swarming': {
-          'shards': 4
-        },
+        'mixins': ['shards-4'],
       },
       'rtc_media_unittests': {},
       'rtc_pc_unittests': {},
       'rtc_stats_unittests': {},
       'rtc_unittests': {
-        'swarming': {
-          'shards': 6
-        },
+        'mixins': ['shards-6'],
       },
       'slow_peer_connection_unittests': {},
       'system_wrappers_unittests': {},
       'test_support_unittests': {},
       'tools_unittests': {},
       'video_engine_tests': {
-        'swarming': {
-          'shards': 4
-        },
+        'mixins': ['shards-4'],
       },
       'voip_unittests': {},
       'webrtc_nonparallel_tests': {},
@@ -136,13 +116,15 @@
       'common_audio_unittests': {},
       'common_video_unittests': {},
       'modules_tests': {
-        'mixins': ['timeout-2h'],
+        'mixins': ['shards-2', 'timeout-2h'],
         'args': [
           # Some tests exceed the default 180 seconds readline timeout.
           '--readline-timeout=1200',
         ]
       },
-      'modules_unittests': {},
+      'modules_unittests': {
+        'mixins': ['shards-6'],
+      },
       'rtc_pc_unittests': {},
       'rtc_stats_unittests': {},
       # TODO(bugs.webrtc.org/11362): Real XCTests fail to start on devices.
@@ -152,7 +134,9 @@
       'test_support_unittests': {},
       'tools_unittests': {},
       'video_capture_tests': {},
-      'video_engine_tests': {},
+      'video_engine_tests': {
+        'mixins': ['shards-4'],
+      },
     },
     'ios_perf_tests': {
       'webrtc_perf_tests': {
@@ -168,12 +152,18 @@
       'common_audio_unittests': {},
       'common_video_unittests': {},
       'dcsctp_unittests': {},
-      'modules_tests': {},
-      'modules_unittests': {},
+      'modules_tests': {
+        'mixins': ['shards-2'],
+      },
+      'modules_unittests': {
+        'mixins': ['shards-6'],
+      },
       'rtc_media_unittests': {},
       'rtc_pc_unittests': {},
       'rtc_stats_unittests': {},
-      'rtc_unittests': {},
+      'rtc_unittests': {
+        'mixins': ['shards-6'],
+      },
       'sdk_framework_unittests': {
         'mixins': ['xcode_parallelization']
       },
@@ -184,7 +174,9 @@
       'test_support_unittests': {},
       'tools_unittests': {},
       'video_capture_tests': {},
-      'video_engine_tests': {},
+      'video_engine_tests': {
+        'mixins': ['shards-4'],
+      },
       'voip_unittests': {},
       'webrtc_nonparallel_tests': {},
     },
diff --git a/infra/specs/tryserver.webrtc.json b/infra/specs/tryserver.webrtc.json
index 0c4b326801..0064e78b3d 100644
--- a/infra/specs/tryserver.webrtc.json
+++ b/infra/specs/tryserver.webrtc.json
@@ -2999,7 +2999,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 2
         },
         "test_id_prefix": "ninja://modules:modules_tests/"
       },
@@ -3048,7 +3049,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 6
         },
         "test_id_prefix": "ninja://modules:modules_unittests/"
       },
@@ -3244,7 +3246,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 6
         },
         "test_id_prefix": "ninja://:rtc_unittests/"
       },
@@ -3589,7 +3592,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 4
         },
         "test_id_prefix": "ninja://:video_engine_tests/"
       },
@@ -3986,7 +3990,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 2
         },
         "test_id_prefix": "ninja://modules:modules_tests/"
       },
@@ -4035,7 +4040,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 6
         },
         "test_id_prefix": "ninja://modules:modules_unittests/"
       },
@@ -4231,7 +4237,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 6
         },
         "test_id_prefix": "ninja://:rtc_unittests/"
       },
@@ -4576,7 +4583,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 4
         },
         "test_id_prefix": "ninja://:video_engine_tests/"
       },
@@ -4973,7 +4981,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 2
         },
         "test_id_prefix": "ninja://modules:modules_tests/"
       },
@@ -5022,7 +5031,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 6
         },
         "test_id_prefix": "ninja://modules:modules_unittests/"
       },
@@ -5218,7 +5228,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 6
         },
         "test_id_prefix": "ninja://:rtc_unittests/"
       },
@@ -5563,7 +5574,8 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
+          "shards": 4
         },
         "test_id_prefix": "ninja://:video_engine_tests/"
       },