Tuesday saw the launch of contactless payment at St Albans City, Harpenden and Luton Airport Parkway on the Thameslink route. Note that it is not accepted at Luton or beyond. With contactless payment already accepted on the shuttle bus from Parkway to the Airport* it means that Luton becomes the 4th airport accessible from Central London using just a contactless payment card.
At the time of writing TfL still haven’t made the fares available either on their single fare finder or my fare finder (yellow button at the top of every page).
As with Brookmans Park, only contactless is available at these stations. No Oyster cards are valid at all. The full range of paper tickets are still available and will sometimes be cheaper, particularly at weekends when super off-peak tickets are valid. In the main single fares will be cheaper on contactless which is particularly useful for the airport. Remember that these out of London contactless extensions are for convenience first, rather than value.
The other important point to note is that there is currently no capping when making journeys that start or end at the three new stations. Depending on the other travel made within London a day travelcard may well work out cheaper.
*Although the shuttle bus accepts contactless payment cards, it does not accept American Express at all.