air-ct5520-k9 Latest Firmware version

[Adnan Jameel]

What is the latest stable firmware version of air-ct5520-k9 WLC. Currently 8.5.131.0 is running. Should I need to upgrade?

Thanks

[balaji.bandi]

As long as it working there is no security issue, you do not need to upgrade.

But latest is 8.10.130 X is Cisco recomendation.

but you need to look also AP matrix if you looking to upgrade by reading the release notes:

https://www.cisco.com/c/en/us/td/docs/wireless/controller/release/notes/crn810mr3.html

[ammahend]

Agree with Balaji, you need to review comparability matrix to make sure upgraded version will support all your APs. 
Given your AP are compatible I would upgrade since Software maintenance support for Cisco Wireless Software Version 8.5 release ended on December 30, 2021.

No patches or maintenance releases will be provided for Cisco Wireless Software Versions 8.5 beyond December 30, 2021.