Google Play Console is now placing a warning sign stating to target to Android Api level 26, though strict enforcement will be applied later this year.
Here is the link to announcement.
When can we expect the update?
New Android Api level 26 requirement from Google
May 09 2018 11:01 AM
I update a new alpha android version and says the same warning:
En este momento, tu app está orientada al nivel de API 25 y debe estar orientada por lo menos al nivel de API 26 para garantizar que se base en las API más recientes optimizadas en cuanto a seguridad y rendimiento.
A partir de agosto de 2018, las apps nuevas se deberán orientar, como mínimo, a la versión 8.0 de Android (nivel de API 26).
A partir de noviembre de 2018, las actualizaciones de apps se deberán orientar a la versión 8.0 de Android (nivel de API 26).
Sugerencia: Cambia el nivel de API al que está orientada tu app. Obtén más información.
This should not be a reason for the drop in downloads that many are experiencing. The keyword is "should not". Google keeps their ranking system secret so it's hard to know exactly what they are doing.
We recognize this is important and we will be getting this out as soon as we can.
If you look only at the Google requirement that new apps use API 26+ by August 1, then no, you don't need to update. Those apps will be fine. Any new apps after August 1 have to support API level 26+. Updated apps have to support API 26+ at some point afterward, but existing apps do not have to be updated.
Now that said, Google has made changes to their "Vitals" program that tracks apps that don't respond, crash, etc. Apps that crash too often or don't respond can get down-ranked. This public release helps improve your apps with regards to Google Vitals, in particular, if you're using ad plugins so you may want to update regardless.
As I understood the notice in Google Play Console, we all have to update apps before 1st November:
Any new apps or app updates published after this change must adhere to these policies. If you have an existing app that's not compliant, you'll need to fix and resubmit the app within 30 days.