Currently, the ACT, along with the states of Tasmania and Western Australia, treat same sex relationships and de facto relationships identically. New South Wales, Victoria, Queensland and the NT treat them equally except in matters involving parenting. By contrast, in the ACT, one can adopt children (usually the same-sex partner's). Only South Australia refuses to recognise same sex relationships at all.
The government is expected to legislate for civil unions, following the New Zealand model. Whether they are called "marriages" or not, the Constitution (Section 51(xxi)) makes marriage a Federal responsibility and therefore legislation would operate only with respect to ACT laws, policies and procedures and would not affect Federal matters such as immigration, taxation, defence and superannuation.