If you stay in pure swift, it's much harder to segfault, but it's still possible, mainly due to the amount of objC code you interact with. Today, it's not reasonable to expect a swift programmer to be proficient without knowing objC, the way it's reasonable for a Java programmer to not know C.

The segfault I hit yesterday had to do with a CoreData API that didn't retained its argument, when I assumed it did. The bug doesn't appear when compiling with -Onone, but does appear in -O. Compiler flags are another place where Swift is still very much in C-land, rather than Java/Python/Ruby land. You still need to understand the C compilation model, and e.g. getting your ARC flags wrong in a cocoapod will still cause crashes.

To be clear, swift is a big improvement over objC, but you can't pretend it's a VM managed language.