Android 12L rolling out to Google Pixel phones starting today
https://www.xda-developers.com/android-12l-rollout/

Android 12.1.0　Build Number:
Pixel 3a (XL): SP2A.220305.012
Pixel 4 (XL): SP2A.220305.012
Pixel 4a : SP2A.220305.012
Pixel 4a (5G) : SP2A.220305.012
Pixel 5 : SP2A.220305.012
Pixel 5a : SP2A.220305.012
https://developers.google.com/android/images
https://developers.google.com/android/ota

Androidセキュリティ速報-2022年3月
https://source.android.com/security/bulletin/2022-03-01

Pixel Update Bulletin? 2022年3月
https://source.android.com/security/bulletin/pixel/2022-03-01