Thank you for helping!

> I'm not clear why you are focusing on hashing user ids. Nor how you landed on a 50/50 split

I landed on hashing and splitting from my research on building A/B tools, but none of that research was targeted towards building real, enterprise products (which is why I asked the question here). From your reply, I take it that this isn't as important as I read about earlier?

> When someone logs in, write a record of which one they got.

I'm confused about what you mean by "which one they got". How do I know which version to assign them? This is what I assumed hashing would solve - we'd have a reliable way to "choose" a version for any given user.

> why assign 50% of an entire userbase to a feature being tested that only 10% of the users touch?

This makes sense, I'm not sure why I had landed on 50%. So the percentage difference does not matter? I had assumed that we need a way to enforce a certain percentage split - how do I prevent a "feature" from only reaching 0.01% of the userbase, whereas the other feature reaches 99.99%?

Thanks again for your reply, you've been really helpful.