This mount costs 2 Platinum 50 Gold.
You can purchase it directly from the Rift Store Mount section.
Can also be purchased from ‘Orobus Vend’ in Freemarch at /setwaypoint 6482 4566 (Defiants)
Can also be purchased from ‘Reynora Skye’ in Silverwood at /setwaypoint 6108 3226 (Guardians)
Can also be purchased from ‘Shria Terke’ in Meridian at /setwaypoint 6151 5211 (Defiants)
Can also be purchased from ‘Nell Hara’ in Sanctum at /setwaypoint 7595 3029 (Guardians)
The ‘Steady’ version (60%) does not Autoscale, this can be useful in some situations.
You can also purchase an account wide unlock of this mount called ‘Escalating Chestnut Horse Bridle’ from the Rift Store.
This mount costs 720 Credits for patron or 800 Credits for non-patron.