Sony starts rolling out Android security patch for the month of January 2020 on Xperia 1 and Xperia 5. Both the phones were launched in 2019 with Android 9.0 Pie. Recently both the phones got Android 10 i.e. the latest Android version.
The update on Sony Xperia 1 comes with build number 55.1.A.0.748 and on Xperia 5 it comes with build number 55.1.A.3.49. Both the phones get a January security patch that includes 35 improvements for the Android operating system. Although Sony did not provide any changelog of the update.
Xperia 1 and Xperia 5 January security update is currently rolling out in the Czech Republic. It will surely come to other countries soon. Anyhow, if you live in the Czech Republic and did not get the update don’t panic, it will reach you in some time.
You can check the update manually by going through the Settings >> System Updates >> Check for updates.