diff --git a/cr-buildbucket.cfg b/cr-buildbucket.cfg
index c4dc0421d..8412e1858 100644
--- a/cr-buildbucket.cfg
+++ b/cr-buildbucket.cfg
@@ -32,6 +32,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Android Debug"
@@ -51,6 +55,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Android Release"
@@ -70,6 +78,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Android Tester ARM32 Debug (Nexus 5X)"
@@ -87,6 +99,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Android Tester ARM32 Release (Nexus 5X)"
@@ -104,6 +120,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Android Tester ARM64 Debug (Nexus 5X)"
@@ -121,6 +141,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Android32 x86 Debug"
@@ -140,6 +164,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Android64 x64 Debug"
@@ -159,6 +187,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Linux Asan"
@@ -178,6 +210,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Linux MSan"
@@ -197,6 +233,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Linux Tsan v2"
@@ -216,6 +256,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Linux UBSan"
@@ -235,6 +279,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Linux UBSan vptr"
@@ -254,6 +302,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Linux32 Debug"
@@ -273,6 +325,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Linux32 Release"
@@ -292,6 +348,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Linux64 Debug"
@@ -311,6 +371,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Linux64 Release"
@@ -330,6 +394,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Mac Asan"
@@ -348,6 +416,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Mac64 Debug"
@@ -366,6 +438,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Mac64 Release"
@@ -384,6 +460,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Win32 Debug"
@@ -403,6 +483,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Win32 Debug (Clang)"
@@ -422,6 +506,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Win32 Release"
@@ -441,6 +529,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Win32 Release (Clang)"
@@ -460,6 +552,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Win64 Debug"
@@ -479,6 +575,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Win64 Debug (Clang)"
@@ -498,6 +598,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Win64 Release"
@@ -517,6 +621,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "Win64 Release (Clang)"
@@ -536,6 +644,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "iOS ARM64 Debug"
@@ -554,6 +666,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "iOS ARM64 Release"
@@ -572,6 +688,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "iOS Debug"
@@ -590,6 +710,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "iOS Release"
@@ -608,6 +732,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
   }
 }
@@ -636,6 +764,10 @@ buckets {
       execution_timeout_secs: 7200
       build_numbers: YES
       service_account: "libyuv-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
   }
 }
@@ -673,6 +805,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "android_arm64"
@@ -690,6 +826,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "android_rel"
@@ -707,6 +847,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "android_x64"
@@ -726,6 +870,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "android_x86"
@@ -745,6 +893,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "ios"
@@ -763,6 +915,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "ios_arm64"
@@ -781,6 +937,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "ios_arm64_rel"
@@ -799,6 +959,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "ios_rel"
@@ -817,6 +981,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "linux"
@@ -836,6 +1004,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "linux_asan"
@@ -855,6 +1027,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "linux_gcc"
@@ -874,6 +1050,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "linux_msan"
@@ -893,6 +1073,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "linux_rel"
@@ -912,6 +1096,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "linux_tsan2"
@@ -931,6 +1119,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "linux_ubsan"
@@ -950,6 +1142,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "linux_ubsan_vptr"
@@ -969,6 +1165,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "mac"
@@ -987,6 +1187,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "mac_asan"
@@ -1005,6 +1209,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "mac_rel"
@@ -1023,6 +1231,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "presubmit"
@@ -1044,6 +1256,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "win"
@@ -1063,6 +1279,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "win_clang"
@@ -1082,6 +1302,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "win_clang_rel"
@@ -1101,6 +1325,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "win_rel"
@@ -1120,6 +1348,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "win_x64_clang_rel"
@@ -1139,6 +1371,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
     builders {
       name: "win_x64_rel"
@@ -1158,6 +1394,10 @@ buckets {
       execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.use_realms"
+        value: 20
+      }
     }
   }
 }
diff --git a/main.star b/main.star
index ecfd0070f..24757c446 100755
--- a/main.star
+++ b/main.star
@@ -21,6 +21,8 @@ GOMA_BACKEND_RBE_ATS_PROD = {
 
 # Enable LUCI Realms support.
 lucicfg.enable_experiment("crbug.com/1085650")
+# Launch 20% of builds in "realms-aware mode", crbug.com/1203285.
+luci.builder.defaults.experiments.set({"luci.use_realms": 20})
 
 lucicfg.config(
     lint_checks = ["default"],