When the SAT was redesigned in 2016, it became much more like the ACT. It used to be that the SAT was more puzzle-like than the ACT, but it's not that way at all anymore.
Probably the biggest difference is that the SAT has more time per item than the ACT. Other differences are that the math section on the ACT goes to a higher level than on the SAT and that the ACT also has a "science" section, which is basically reading comprehension with graphs and tables. I put "science" in quotes because if you are using what you know about science to answer the questions, you're probably going to get them wrong.
