While no ingredient in Soylent Powder or Drink naturally contains gluten, the oat flour is produced in a facility that also processes wheat products. Although there is an allergen contamination program in place at the facility, the final mixture of Soylent is tested to have more than 5 parts-per-million of gluten, the concentration that the Celiac Support Association requires in order to certify a product as gluten-free.
The cross-contamination challenges of oats are significant. From the farms where they are grown, to the products they are included in, oats have numerous opportunities to come into contact with surfaces that have also come into contact with wheat, barley or rye.
Furthermore, avenin, the storage protein found in oats, poses additional challenges. Due to the similarities of the amino acid sequences of avenin to those in gluten, avenin can sometimes cause gluten-like immune responses for some people who have Celiac Disease.
The Celiac Support Association website hosts one study and links to several others on oats and Celiac Disease:
We're researching several promising alternatives to oat flour, but at this time we haven't yet identified a suitable replacement.