Short version: the 1983 Diet Squirt and today's Squirt Zero Sugar appear to use the same core sweeteners, aspartame and acesulfame potassium, and the label changed mainly in name and packaging. I found no published record of the full formula history, so I can't say how much the recipe has shifted.
For the 1983 Diet Squirt, the Wikipedia entry on Squirt) says it was the first US soft drink sweetened with aspartame. A vitamin-C version, Diet Squirt Plus, was briefly sold in the mid-1980s. Squirt's own retailer listings now say "Diet Squirt is now Squirt Zero Sugar," and the ingredients they list are carbonated water, grapefruit juice concentrate, natural flavors, citric acid, aspartame, acesulfame potassium, modified corn starch, ester gum, sodium benzoate and calcium disodium EDTA. The exact date of the rename isn't clear from what I found.
The ingredient lists don't fully agree. One Foods Co. listing also includes brominated vegetable oil, while a Safeway listing for the same product doesn't. That likely reflects different batches or markets, so check the can in your hands.
For the original formula, the sugared Squirt has used high-fructose corn syrup, and the brand has always claimed less grapefruit and sugar than rival sodas. Sources give different grapefruit figures, with some saying under 1% and others under 2%, and I couldn't find a reliable record of how the recipe changed across decades. A comparison of taste from the 1980s would have to come from people who drank both.
If you want firm dates for the formula changes, Squirt's own history page or a food-industry archive would be the place to look.
🕒 As of November 2026