Ask HN: In CS, is it better to be highly specialized or generalized?

As a programmer, is it better for long-term career growth to hone in on one single skill (i.e., systems programming, or high-performance computing, or webdev) or is it better to be more of a generalist - to be able to write iOS apps, but also know a bit of assembly, but also be familiar with .NET and React, etc.?

To rephrase: should a software dev be a jack of all trades, or a master of one?