When you get your brand new Cisco ASR1000 series router, Stateful Switchover (SSO) is disabled by default:

Router# show redundancy states
       my state = 13 -ACTIVE 
     peer state = 1  -DISABLED 
           Mode = Simplex
        Unit ID = 6
Redundancy Mode (Operational) = Non-redundant
Redundancy Mode (Configured)  = Non-redundant
Redundancy State              = Non Redundant

Enable SSO!

Router# config t
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)# redundancy
Router(config-red)# mode sso
Router(config-red)# ^Z
%CMRP-6-DUAL_IOS_REBOOT_REQUIRED: R0/0: cmand:  Configuration must be saved and the chassis must be rebooted for IOS redundancy changes to take effect
Router# reload

And once it's back live, you can see that SSO is up and working:

Router# show redundancy states
       my state = 13 -ACTIVE
     peer state = 8  -STANDBY HOT
           Mode = Duplex
           Unit = Primary
        Unit ID = 48

Redundancy Mode (Operational) = sso
Redundancy Mode (Configured)  = sso
Redundancy State              = sso
    Manual Swact = enabled
 Communications = Up

   client count = 87
 client_notification_TMR = 30000 milliseconds
          keep_alive TMR = 4000 milliseconds
        keep_alive count = 0
    keep_alive threshold = 7
           RF debug mask = 0x0