Try it here: https://jegy.mav.hu/jegy/reszletes-kereso

It's listed and seems to be bookable.

Hi @wattleflower01 You can try booking using https://shop.oebbtickets.at/en/ticket. Just be sure to indicate you have a Pass where it says 1 xAdult without a discounts.

@St Kristoffer That doesn't work because the train isn't listed there yet (see OP). 

You need to use https://jegy.mav.hu/jegy/reszletes-kereso if you'd like to do a reservation right now.

Only other option is to wait. 

@Hektor when you say wait, do you mean that eventually Eurail will have this specific trip listed on their booking page when it gets closer to the month of Jan? Just want to rule out if there is any changes to the route. 

Thanks all for your help with this

I think, the problem with this train is that the hungarian operator MÁV didn’t deliver data for this train yet (because it isn’t in any other operators app). The fact that it is listed in their own app is a signal that it will run (they should know best). And as I did write: It’s even possible to book it (even with an Interrail pass; but of course I didn’t try to pay, so there may be an error message in the end, too).