Domestic SNCF tickets are available 3 months in advance. SNCF tickets to and from Italian destinations are available 4 months in advance. Prem's are cheaper French train tickets that are available on all TGV (French: train grande vitesse), Intercités, and TER trains. They are extremely popular and sell out quickly, so we recommend making your reservation as soon as possible.
TGV Lyria (France - Switzerland)
Opening of ticket sales in 3 words:
Anticipation: TGV Lyria train tickets are available up to 6 months in advance to the day.
Adaptation: If there is planned track construction or a change in the timetables, the date of availability of the tickets may be affected. Please check TGV Lyria’s traffic information page beforehand.
Action: There are a limited number of seats available at low prices. Less expensive tickets sell out quickly, especially on high-demand routes during peak season or at peak times.
In short, be prepared so that you can plan your trip at the lowest prices.