Yes.
Joining the Pension scheme is mandatory for all Government employees.
The major change has been in the type of pension scheme. Prior to 2004, the scheme was defined benefit scheme, i.e the pension you would get after your retirement was defined when you join the service itself.
After 2004, the scheme is contributory, where the government and the civil servant both contribute to a corpus that will go on to make the pension that will be paid to the civil servant when he retires. This corpus is managed by different fund managers, who invest it in different market instruments like equities, corporate bonds, government securities etc. The returns that your corpus will generate will depend on the market conditions at the time of your retirement.