A thought I had recently was to shift from having candidates write code to have them review code. I'm sure it's not an original thought, but it comes with a few advantages. 1. Reading someone else's code is usually harder than writing your own and in most projects you spend more time reading code. You're seeing how they'd handle the more common work. 2. You can still pick how deep you want to go in the interview. Like some of the algo problems where interviewers keep adding new requirements, you can discuss API design, performance trade-offs, other code qualities. 3. You get to see how respectfully they can discuss a future colleague's work and how well they can communicate their own ideas.
Some of the very productive developers I have worked with are not great at code reviews. It's a different skill from writing code and not everyone who is good at coding is good at reviewing other people's code.
Considering most of us spend about 90% of our time coding and a very small amount of time doing code reviews, your best signal in my experience is just giving candidates something to code.
