Gluten free hosts are not offered at any Mass. There are low gluten hosts, but no “gluten free” hosts.
The low gluten hosts are made from a recipe of wheat starch and water, approved by the United States Council of Catholic Bishops as valid matter for use in the Catholic Eucharist according to canonical requirements. Gluten content of the brand that most parishes in our diocese is below 20 parts per million.
However, if someone is truly celiac (tested, diagnosed and monitored blood work), they need to let the priest or deacon know before Mass that they need a low gluten host. They should have a special clip on tray for the ciborium and when you approach, you should indicate that is for you. But realize that unless he washes his hands, you are going to be exposed to gluten from the other hosts he has touched.
Sometimes the faithful in our parish will request to receive only the Precious Blood, even if it is not offered at that Mass. A chalice is prepared just for them and the priest sends the altar server to retrieve it when the person approaches. That ensures no cross contamination.