If you want to travel with the panorama coaches of the Bernina Express, you need to book compulsory reservations through the site of the Rhätische Bahn: https://shop.rhb.ch/en/bernina-express All the seats offered through this booking engine are for the panoramic coach.

While first it will show the price of both a train tickets and a reservation, in the "traveller details" step of the booking process you can indicate "Eurrail pass" (sic) as a discount card which removes the ticket costs.

Note however the non-panorama coaches don't require any reservation for Eurail passholders, and also offer pretty decent views. 

You can find more details here: https://www.eurail.com/en/get-inspired/trains-europe/scenic-train-routes/bernina-express

If you want to travel with the panorama coaches of the Bernina Express, you need to book compulsory reservations through the site of the Rhätische Bahn: https://shop.rhb.ch/en/bernina-express All the seats offered through this booking engine are for the panoramic coach.

While first it will show the price of both a train tickets and a reservation, in the "traveller details" step of the booking process you can indicate "Eurrail pass" (sic) as a discount card which removes the ticket costs.

 

Note however the non-panorama coaches don't require any reservation for Eurail passholders, and also offer pretty decent views. 

You can find more details here: https://www.eurail.com/en/get-inspired/trains-europe/scenic-train-routes/bernina-express

I was navigating through the website and manage to get to this page. However, I was wondering if I am eligible to book a 1st class seats if I have 2nd class Eurail Pass because it doesn’t specify terms&conditions on the website regarding Eurail pass holder eligibility. Both seating class also have the same booking fee. 

Basic principle: for 1st-that usually means wider seats and nothing else, one needs a ticket or pass for 1st. In SOME areas/countries it is possible to do a 1 time upgrade by paying the difference in NORMal fares from 2nd to 1st-mostly that means 50% of full fare-and it is Swiss, so that can be astronomically high. Easy to check this cost by doing a dummy booking for the whole sector for 2nd-then 1st-you intend to make on them. That is- IF they even allow this, I am not sure about that.  That prices for the RES are same says nothing, but seems as many ask about it lately a common misunderstanding. This cost is simply the cost of the administration to do this and in the end show a tiny paper or electronic set for that seat on that day. Thats all!

2nd class passes NEVER allow you to just sit in or buy a reservation for 1st class accommodation.

It in some cases is possible to buy an upgrade but there is no online booking that I know of that allows this.

@Jamie Wach @Schelte @Al_G @mcadv 

Here is information about how to make an upgrade from 2nd to 1st class in Switzerland.

https://www.sbb.ch/en/travelcards-and-tickets/tickets-for-switzerland/class-upgrades-supersaver-class-upgrades/class-upgrade.html

Interesting. Looking at the prices for these journeys, I expect exchanging your pass to a 1st class pass (€15 fee + price difference) will be cheaper. 

I in fact only know SNCF allows upgrading reservations on their domestic French TGV & Intercités services. These can be made on online and automatically appear as you fill in a 2nd pass in the search engine. Funnily, it is sometimes cheaper to buy an upgraded €10 reservation than a 2nd class €20 reservation. That's the only exception I know where this is integrated with the reservation process.

For domestic French reservations, that is possible via Belgian railways:

https://travel.b-europe.com/Eurail-GE/en/booking-tgv#TravelWish