There are some changes to which levels allow one versus two hands on the reins. The new rules allow the use of two hands all the way from Children’s through Level 5.
It is important for correct training to use two hands a large portion of the time. However a working horse must also be obedient and responsive to one handed riding. Since many of the obstacles require the use of one hand on the reins, all levels are encouraged to practice riding one-handed as well as two handed.
Below is the excerpt regarding Use of Hands.
1.11 Use of Hands Horses may be ridden with one hand or two in all levels up through Intermediate B (L5). All trials in Advanced (L6) and Masters (L7) levels must be performed with the reins in one hand.
Competitors are free to use either hand to hold the reins, but may not, under penalty of disqualification, switch hands or use their other hand on the reins during the trial. Competitors will be disqualified if their free hand brushes the rein in front of the rein hand or provides any form of assistance. An adjustment to the reins is permissible but must be a momentary action, with the free hand touching behind the rein hand. Holding the excess rein in the free hand during the trial is not allowed (exception: western riders using a romal rein or knotted/connected split reins may hold the excess rein loosely with the free hand).
Competitors may use either the right or left hand when negotiating obstacles in EOH and Speed trials; however, the same hand must be used consistently for every obstacle under penalty of disqualification