they’d had Vistara as an option for quite a while - I’d guess a year to a year and a half that I’ve seen, just on UK flight numbers. Definitely when Jet was still operating. Can’t remember exactly though on timing. I’ve definitely seen DEL-MAA/BLR (that’s tyoically where I fly) and I think some BOM frequencies too (haven’t looked beyond that as I typically fly to one of those two). Don’t know about bag check through, as I never ended up using UK, but it seems to expand the partnership to allow codeshares and mileage accrual. I’m guessing bag check through doesn’t work on US-India, as UAs flights likely wouldn’t connect same day to UK flights.

Definitely want to try Vistara though. AI is decent domestically, but all the other Domestic India options aren’t good, and Hopefully this could be a good option.