Originally Posted by
ChocolateFactory
This has already been answered in the past.
Basic economy is not a different class of travel (after all, it’s the same seat), so you have to figure out the booking classes for your specific airline and then filter based on that.
There is no way for ITA to know if a fare is “basic” or “regular” economy.
Even that doesn't always work. BA offer same fare bucket (say L) as Basic which is handbaggage only or Plus with checked bag and free change on day of travel. Hence my question as to what sub-OP was looking for. ITA can find L availability and will give Plus price. Basic can then usually be booked as well at chosen point of sale.