This is from the current website concerning the Prague>>Budapest run.
"There is absolutely no need to book further ahead that this, you can usually find the cheapest fares even booking just weeks ahead"
I was misled by a similar statement posted on his website for an Austrian train in 2015. Prices rose then with a week or two of being offered (4 months out). Right now on this run prices for summer travel jump 25% within 2 days of going on sale 90 days in advance. You absolutely CANNOT get the cheapest fares "booking just weeks ahead."
Noting that for a German train I was following, the prices also jumped 25% within 2 weeks of going on sale 120 days out.
For whatever reason the Czech Railway is offering free seat reservations right now in second class.