If you're referring to 8.0, no info on that link means Samsung haven't sent it to Optus to test yet
Sammy pulled the Oreo update as it was causing random crashes and reboots, lag and a few other niggles.
I think you can still get a copy, and flash it with Odin. Ironically the firmware ends in the letters CRAP, though with all the issues, I'm not sure why you'd want to.
I do wonder when the monthly security update will come out, as mine is still on October, and I check daily if anything is available but nah.
To be honest it's a good phone but I'll be going back to a Google based phone next time, or at least one that runs stock Android and gets the regular updates when they're released.
Samsung has begun re-rolling out the Oreo update.
With regard to Optus not receiving it.... They should have by now.
You can use Odin to flash the CRAP firmware then install the latest 500mb update.zip. There's a fair few threads if you google the info