Yes, but it is the firmware that is specific to handling Zigbee and often referred to as the ‘stack’. It can be installed independently of the hub firmware and appears as the ‘Zigbee version’ when you view the hub in the IDE. I don’t think you can see it in the app.
I have two V2 hubs so can’t vouch for other hub versions, but …
The hubs have been on Zigbee version 2.9.0 for quite some time. It was apparently updated to 5.1.2 for those beta testing version 35.x of the hub firmware but not pushed out into production.
I enrolled one of my hubs into the beta program in time for version 36.x of the hub firmware and the Zigbee version was updated to 5.1.2 prior to my receiving the hub firmware. It was subsequently updated to 5.2.1. It was not pushed out when version 36.5 of the hub firmware rolled out into production.
Within 24 hours I found most of the IKEA On/Off (aka Dimmer) buttons I had on the hub no longer responded. One or two still worked. One or two could be paired again and worked. The others needed new batteries. Within another 24 hours all the buttons that hadn’t received new batteries had now failed in the same way, and so had some with new batteries. Those buttons remaining on my other hub remained fine. Over the next day or two I got through two or three batteries per button and so switched all but one back to the other hub where they remain (I have since added another to the beta hub to provide more data).
ST swapped my beta hub back to the old Zigbee version and the buttons were happy again. Then back to the updated version and they lasted 24-48 hours. Now back on 2.9.0 and they are still working.
A secondary issue was that I wasn’t seeing battery reporting on some buttons. I know that disappeared from the event history several months back but the attributes themselves remained null. ST noted communication errors had blocked the battery configuration commands. Power cycling the repeaters (Tradfri outlets) the buttons were communicating via and pairing the buttons again dealt with that. However that happened on both my hubs.
I don’t know if this is an ST or an IKEA issue, or neither, or both. It is making me rather nervous though. I need ST and IKEA to be best friends.
Update: Corrected version numbers.