Just to clarify that reservations are not obligatory. Zweisimmen – Montreux is really the only true ‘Golden Pass’ line, see my ‘faq’ I developed as a cut and paste as this query crops up time after time. :
Current tourist branding can be confusing
The true ‘Goldenpass line’ is just the MOB railway Zweisimmen – Montreux. The Luzern – Interlaken railway is actually the Brunig Pass.
The Luzern – Meiringen – Interlaken line is the Brünig pass line operated by Zentralbahn (ZB), which dubs the regular trains “Luzern – Interlaken Express’.
A few facts about the Montreux – Zweisimmen railway – ie the MOB (Montreux-Oberland Bernois):
The Golden Pass is historically only Montreux – Zweisimmen, only more recent marketing branding takes the ‘Goldenpass route’ east of Zweisimmen to Interlaken and beyond to Luzern.
The Golden Pass is the touristic branding for the Montreux – Oberland Bernois (MOB) railway which runs from Montreux to Zweisimmen, but after a few years of favouring ‘Goldenpass services’, the company decided it was losing its tradition and has reverted to putting the Chemin de Fer Montreux – Oberland Bernois name on publicity and train coaches.
MOB pioneered the Panoramic coach concept on Swiss trains, starting in 1976.
There are now several versions of panoramic coaches in service, but MOB keeps changing its mind how to dub each service.
It hardly matters anyway as most modern Swiss trains have large windows, even if not officially panoramic. The key element of a ‘panoramic’ coach is ‘toplight’ windows above your head but in practice very few of the major views from panoramic trains are directly above your head, so the view through the normal side part of windows is normally fine.
You can really use any through train on the MOB. Again, this gives you the flexibility to get on a train at whichever time suits you.
It is very scenic, but the MOB route is far from being the most spectacular (although any dubbing of this nature is going to subjective and personal) in Switzerland.