The Commonwealth Superannuation Scheme (CSS) closed to new members on 30 June 1990. I was in that scheme and when it closed we were offered the choice to go to the then new Public Sector Scheme (PSS). It was still a Defined Benefits Scheme but in my circumstances, over 15 years of employment, not as desirable as the CSS. The PSS itself was closed on 30 June 2005.
There are all sorts of permutations regarding untaxed and taxed components but I do pay tax on my income from the CSS at my marginal rate but with a 10% offset.
If you want a read then -
https://csc.sitecorecontenthub.cloud/api/public/content/567195f0cd5544deab236b1f3e35820b?v=dfebf1b3