There are several groups doing epidemiological modelling but for different purposes.
In Victoria, we used two agent based models by groups based at Burnet and Uni of Melbourne to help plan our path out of lockdown. Despite their limitations and different approaches/assumptions, they were quite helpful in exploring the potential risks associated with various opening up options. I think even the people involved would admit they were surprisingly accurate (to the day!).
I don't know as much about the Sydney modelling, but I'm aware that there have been discussions between at least one group and NSW Health.
Additionally, a consortium of modellers (including the Doherty group) have been estimating the effective reproductive ratio and "transmission potential" from a range of data sources, including case counts, mobility data (Apple, Google and Facebook) and community surveys of compliance. The estimates are reported in the Common Operating Picture each week.
Delta - during Melbourne's June lockdown, there was an outbreak of the delta variant centred on a primary school and the workplaces of associated families. The index cases in this outbreak (the Jervis Bay campers) were fortuitously detected while Victoria was already in lockdown due to another outbreak (with the kappa variant).
And of course, the current July lockdown in Victoria, hopefully due to end today, is a result of a delta incursion from the famous removalists from NSW and has involved more than 170 cases.