Yes, this is gluten free
Gluten-free. Made by fermenting a sugar feedstock — usually corn, molasses or cassava — then crystallised out and purified, which leaves no protein behind. The old warnings about it were never founded.
A small organic acid, the thing that makes a lemon sour, and almost none of the commercial supply comes from lemons any more. It is made by feeding a sugar solution — usually corn glucose, molasses or cassava starch — to the mould Aspergillus niger, which excretes citric acid into the broth. The acid is then precipitated, recrystallised and purified away from everything else that was in the tank.
Because it earned a place on a generation of hidden-gluten lists that circulated online, on the reasoning that the fermentation feedstock might be wheat. The feedstock rarely is, and the inference does not hold even when it is. The lists outlived the reasoning, and citric acid is now one of the most commonly avoided ingredients that has never been a problem.
Nothing. Do not avoid it, do not ask a manufacturer about it, and do not count it as a possible cause when something has gone wrong. The more useful thing to take from this entry is diagnostic: a list that tells you to avoid citric acid is a list assembled from rumour rather than from how the ingredient is made, and whatever else is on it deserves the same suspicion.
CiCi returns citric acid clean with no hedge attached. Adding a soft caution would cost nothing to write and would quietly subtract several hundred products from somebody’s groceries in deference to a claim that was never true.
Point CiCi at the barcode on the product you're holding and get this same reasoning in about two seconds, plus the carbs and the full nutrition panel. 360,000+ packaged foods are already read and waiting.
This answer comes from CiCi's ingredient lexicon — the same rules the scanner uses, not a separate article. Where reputable sources disagree, CiCi takes the conservative position and says so.