when you say still free, it is only very recently when the tube has become free between LHR stations and Hatton Cross. For as long as I remember it was not free on the tube (although when there was a free bus zone it was free on the bus to Hatton Cross).

But yes with the recent changes it is free to travel from any LHR tube station to Hatton Cross. You tap in and out as usual with an oyster or contactless card, but you won’t be charged.