“The pot it’s in is causing it to be root bound and stunting its growth.” No, the pot is highly unlikely to be causing it to be root bound. Root bound means the pot is completely full of roots with them growing around and around the perimeter of the pot and strangling itself.

The pot may very well be the problem, but not due to roots being bound.

Here’s a root bound plant.

It will take a while for that Sans to fill the pot, but I think it's the right size and a really cool pot and will be perfect for it when it's mature! I just hope the pot has drainage holes.

Eventually it will fill the pot after several years.

February in a cool room in the basement.

outdoors for summer in bloom. Needs some grooming but maybe one of these days/years.

It's hard to see much of your pot and exactly how big it is. Also, it's hard to see what the root ball looks like. For myself, all I can do is share with you my experience with Sans. I have 7 or 8, although not many trifasciata like yours.

I keep all my Sans in plastic pots, mostly because of the weight of the pots when filled. Also, a strong Sans WILL BREAK through a plastic pot in trying to grow. (That's always a good sign -- give it a new pot to grow bigger!) I think your pot may be a bit large for the single cutting you received, although it clearly has an under-soil rhizome that is growing sending up a new pup, a good sign. Personally, I would leave it alone right now, in the growth stage, see what happens next year. You can always repot in March or April.

My Sans do best in snug pots. Most important with Sans, I believe, is the medium. LOTS of people here grow in mixes that have no soil, no organics. I haven't had great success doing that. I myself grow in a blend: about 40% cactus/succulent soil and 60% pumice (or you could use perlite). I like an organic soil but a gritty and aerated soil for my Sans. And they are very forgiving, so DON'T over-water. The Sans I have destroyed have been largely from TOO much attention and TOO much watering: the kiss of death for a Sans.

Pot is okay if you watch your watering. Main reason we use small pots. It drains much easier and less chance of over watering. By all means go bigger if you want.

The more room roots have to run, the better; however, how large the pot can/should be is determined by soil choice. Example: If you are growing in a medium that looks like this,

your sans could be planted in a 55 gallon drum filled with soil and not suffer from any of the limitations the average grower associates with over-potting. "Over-potting" is a term that only holds currency if you are using a water-retentive medium, one which holds any notable volume of water in the spaces between soil particles. What determines whether or not a medium can/will hold water in the spaces between particles is the size of the particles and the ratio at which different size gradients are combined.

Snug pots and root congestion are stressful and limiting, so the idea any plant does better in a smaller pot is wayward thinking, at least from the plant's perspective. Root congestion begins to take a toll on a plant's potential in areas like growth rate, vitality (health) and appearance at the approximate point in time when the root/soil mass can be lifted from the pot intact. From that point forward, there is a direct relationship between factors growers normally concern themselves with and the increasing severity of stress root congestion imposes. How someone cares or doesn't care for their plants shouldn't bother another, but that is no indication it won't 'bother' the plant.

The thorns of this MP tell a story about the plant. Starting from the soil line and moving up, you see a definite change in the distance between thorns about half-way between the soil line and where the plant branches. That marked change represents the point in time where the plant was potted up. Moving upward slowly, you'll see the thorns again become closer together until the next major intervention which was removal of the top of the plant, and, another up-potting. You can tell it was up-potted a second time because the thorns on the 3 second order branches reverted to the wider spacing you would expect after potting up.

Had the plant been repotted (bare-rooted/ root-pruned/ soil changed) on a regular basis instead of having been potted up, the size of the plant in terms of extension growth and o/a mass would have been many times greater (probably 6-10) than what it is in the image because there would have been no stress to limit growth. On a scale of 1-10 with 10 being best growth potential, repotting returns the plant to a potential of 10 every time, where potting up is only capable of easing stress enough to allow the plant to realize much less than 50% of the potential afforded by repotting ..... which is why it's a half-measure band-aid fix.

BTW - for most of the US, March and April are very poor months to repot in. Plants are at their weakest after a long winter (unless you've used good supplemental lighting. Repotting plants when their stored energy is at low/lowest ebb and current ability to create food/energy is still very low do to short days/low light intensity, ensures a long recovery during which plants will be much more susceptible to disease pathogens and insect infestations. It's much, much better to work WITH the plant's natural rhythms and repot in June (for all but the Deep South States) when stored energy levels are highest and current ability to carry on photosynthesis is also peaking. Think Father's Day or the Summer Solstice as a way of remembering when houseplants are best able to deal with the stress of hard work like repotting and heavy pruning.

Al