Optim callback function -- how to use optimization variable

The optim callback function seems to operate on the OptimizationState, which provides access to the iteration count (.iteration) and value. Can I access the optimization variable being optimized (i.e. temporary optim.minimizer(res)) ?

A bit late to the party, but I’ve replied to the same question here. (Adding a cross-ref in case somebody searches for the question online and ends up here.)