Classic, to wit, "traditional".
Since 1998 or 1999, the shift was to 8 epsiodes. Now there has been a shift to 10, 11, or 12. Depends on the show. Still uncommon to see a series length over 8 unless it's a flagship show.
Each series of Red Dwarf was 6 eps, except 8. (And Back To Earth, which was piss). Thats 6 from 1987 to 1997 IIRC. And 8 for 1997-1999. If they were to another one now, no way it'd be more than 8.