zpool autoexpand feature is absent

Hi!

what can be the reason that the zpool autoexpand property is missing?
It's a system running Solaris 11.3 SRU 19

$ zfs get all rpool

NAME PROPERTY VALUE SOURCE

rpool aclinherit restricted default

rpool aclmode discard default

rpool atime on default

rpool available 403G -

rpool canmount on default

rpool casesensitivity mixed -

...

$ zfs get -H -o value autoexpand rpool

bad property list: invalid property 'autoexpand'

For more info, run: zfs help get

$ zpool upgrade -v

This system is currently running ZFS pool version 37.

On a similar system running 11.3 SRU 35, and also zfs version 37, I can see this property.

-- Fritz