It was mentioned initially in this forum post. I had to search for the details on Kogan Mobile for confirmation
Similar to the free 5G trial rollout from Boost, credit to @tightarse for the title format
What is the 5G Trial?
We are offering a 5G access trial to eligible new and existing mobile customers who sign up to our Large and Extra Large 365 days plans, Large and Extra Large 365 Flex plans, and Extra Large -12 Months plan or are already on our Large and Extra Large 365 days plans, Large and Extra Large 365 Flex plans, Extra Large -12 Months plan, Large and Extra Large 30 days plans, Large and Extra Large 90 days plans and Large and Extra Large 24 Months plans. This means that all eligible customers will have access to our 5G Network if they have a compatible 5G phone and are in a 5G coverage area, until 26 October 2022, unless extended further.
Not all plans, only Large and Extra large plans.