Have you ever heard of Generation UCAN? It claims to be sugar-free, not necessarily low-carb though (so not sure this is quite what you're looking for).
View attachment 279063 View attachment 279064
I attached the scientific white paper (pdf) from the Generation UCAN website.
Here is Runner Connect's counter-point as to whether its real or skirting science:
https://runnersconnect.net/ucan-marathon-nutrition-review/
I know of one person who uses it and highly recommends it. I haven't used it before, because it can get pretty pricey.
If you decide to try it, you can get it at a discount by using the website associated with McMillan (
link).