From the interface (mostly yes, that, is apart from the impure extensions added later, and that chars are used and not codes) it is the same. But from the implementation behind it´s different. In particular from the space requirements. A text of n characters requires 3 * 8 * n bytes in SWI, but n + 2 * 8 bytes in Scryer. So there is a factor 24 in space requirements (on 64bit).

Also, there is now ample room for input that SWI once almost offered.