Everyone calls class 9 'the foundation year'. What actually changes from class 8?

Class 9 for my son from June. Every relative, every tuition centre flyer and his class teacher at the last PTM has said the same thing: class 9 is the foundation year, take it seriously. Fine. What specifically is different? More subjects, harder maths, a different exam pattern, more weight on internals? I want the actual changes, not the slogan, so we can plan the year without panicking him.