What kind of tools that Facebook uses for A/B testing?
Are they doing trunk-based development?
There are generally 2 ways to do A/B testing at Facebook (note: Meta is so large now that I'm sure various orgs may have built specialized tools at this point):
There's a bit more nuance around things like experiment setup, universe setup, and how long your experiment needs to run.
What do you mean by "trunk-based'? Almost everything at Meta is going to be based off mainline. There are very few long-lasting feature branches.
Meta-question: Why are you curious as to how Meta specifically does A/B testing? Is it because engineering leadership at Sinch wants to emulate Meta specifically?
I'm not sure if trying to copy what Meta will make sense as it's operating at a much larger scale than anything you're working with, which leads to far more complexity in the tooling. I recommend working backwards from your needs, building the simple thing first, and iterating from there.
If you want to learn more about experimentation at Meta though, I left a lot of thoughts in this discussion from a Meta engineer.