Pretty sure most don't. Most A/B Test SAAS vendors cater to lightweight clickstream optimization, which is why they don't have features like Stratified Sampling. Internal systems are lightyears ahead of most SAAS vendors.
I work at Statsig and we built it recently: https://statsig.com/updates/update/stratified-sampling. Definitely still some internal systems that are way ahead of SaaS but we're seeing more companies ditch internal builds for us.
