From the Sound Bar

While the sound bar is in Sleep mode (LED is blinking), use the sound bar remote control and press the following button in sequence: Forward Arrow >>| Rewind Arrow <<| VOL down -. The sound bar will display a series of alphanumeric values, the most important digits are displayed after the 'WAIT' text Dxxxx. In the sample video below, it shown D0204 which indicates the main software version is 2.4.

Via the Google Home App

If you have linked your Alto 9+ to your Google Home app then you can easily view the sound bar's software by following the instructions below:

Launch the Google Home app Tap the name of your  Alto 9+ sound bar
Press the Settings icon, this will open the Alto 9+'s Device settings page Scroll down to the Information section, you will find the System firmware version - as shown on the image on the right>>>