Bitmain Antminer S9k (13.5Th) - Latest firmware

Hi, Bitmain

I have the Bitmain Antminer S9k (13.5Th).

The miner can still connect to the mining pool and the software still of 2017 is still running.

What is the latest mining software for 2021 for this miner?

As I am not even getting an error on the boards that they are not working.