It’s not sold out. The reason why you won’t get a reservation is that there is track construction going on on this route and all direct trains will get a new timetable between Linz and Budapest that is not confirmed yet. To do a reservation, you may use Tickets & services (oebbtickets.at), but there will be a revised timetable and you need to wait until it is confirmed (no date announced for this).

It’s possible to do a reservation for trains that don’t go directly (e.g. starting in Wien for Budapest), but of course this is less convenient and you don’t know exactly when you’d be arriving in Wien by connecting trains.

BTW: There’s no mandatory reservation on this route. You may also board without a reservation. So it will be no problem to do this trip at all.

Bookable in DB Navigator

Bookable in DB Navigator

That won’t work. It’s just shown because Westbahn has still a not revised timetable.

Thank you, Hektor. Very informative. We still have a dilemma, however. Can’t buy Eurail passes until this leg of the trip accepts seat reservations.  But your reply answered a lot of my questions. and thank you again.  We are considering mydaytrip.com as an option if this leg does not open up. 

But as written: It’s no problem to do this trip. You don’t need a reservation and as noone else is able to buy it yet it’s still an empty train. No need to worry even if reservations do open late...

Thanks, Hektor.  We want to buy first class global Eurail passes so that we can reserve seats.  For the Munich to Budapest train at issue, is it first come first serve for seating in first class?  Thank you again. 

If you don't hold a reservation, it's first come first served even in 1st class. Reserved seats are indicated. For a surcharge of 15 € per person, you may also use business class when holding a 1st class pass (much better experience).

Thanks again, Hector.  Much appreciated.