Are there any guidelines to the ratio of brown sugar to cinnamon to xanthan gum to get that gooey texture in cinnamon rolls? I'm trying to make cinnamon rolls and want the perfect filling. :)
I have been making cinnamon rolls professionally for 10 years. I have done both traditional cinnamon rolls and gluten-free cinnamon rolls, and the only time xanthan gum was included was in the dough for the gluten-free rolls. Normally the inside is gooey because the butter and sugar (and some moisture that the sugar pulls out of the dough) combine and form what is basically a heavy syrup inside the roll (cinnamon also contains/releases some gums of its own, but their effect is probably negligible due to the short cooking time). Xanthan gum would function to make sort of a sauce of your smear, but there really shouldn't even be enough moisture there for the gum to absorb.
If you're having trouble with the smear sinking out of the roll as they cook, you can try using less butter in your smear, or just using sugar and cinnamon and only brushing the exterior with butter. Butter melting will cause separation between the layers, whereas the sugar cooking will stick them together. A far out option would be to include some powdered sugar to help soak up the extra moisture (but again, just don't include extra moisture!). Xanthan gum shouldn't be necessary at all unless you're making a recipe specifically to be frozen raw or trying to make a separate caramel sauce (which still shouldn't need it!)
Since the question now appears to be specifically about Cinnabon cinnamon rolls, according to one of their spokespeople, they don't include xanthan gum. They do include both invert sugar, which helps to keep sugar syrups smooth and is very gooey on it's own, and modified corn starch, which is a thickener and gelling agent. A lot of ingredients in a commercial product, like Cinnabon, are only there for ease of handling such large quantities and to help ensure consistency in freezing, thawing, shipping, etc. For instance, if you were going to mass produce dough and freeze it, you'd need azodicarbonamide to keep your dough supple. Making dough at home or in a restaurant, there would be no advantage to using it. As such, the usage level is usually between .25% and .5% for most gums, but the usage would be based more on how long the dough is frozen, how quickly it's frozen, etc rather than a ratio with other ingredients.
Classic cinnamon roll recipes do not include xanthan gum or other extra stabilizers in the filling recipe. As SourDoh relates, they primarily rely on the caramelization of the sugar as a binding agent and to a lesser extent the gelling action of the cinnamon itself.
This doesn't make it wrong to add xanthan gum to the filling, but it does mean that it is less common, and there is no single classic ratio to rely on. There are several modern recipes circulating which do use xanthan gum in the filling (and some that include cornstarch), in particular, Cinnabon clone recipes.
Reading through a heckuvalotta recipes, I'd recommend that you do not want more than 2 tsp xanthan gum or 1 Tbsp cornstarch for a filling with about 1/2 c butter or margarine and about 1 c brown sugar. Some recipes use less xanthan gum, some use more cornstarch. I think more than this amount will make it more gluey and less gooey, and might start to affect the flavor. You could very easily use half of that.
I haven't tried this method myself, though. This is just a survey of reading a lot of recipes and the comments from users on those recipes.