JSA's Mumbai office follows (or rather used to follow) this approach generally: First they'll offer you a 4-week internship. At the end of your internship, you prepare a worksheet where you write the name of the attorneys you've worked with and the work that you've done for each of them and submit this to HR. HR circulates this sheet to the attorneys to get their feedback on your work. If it's good, you get a callback for a second internship, which could be anywhere between 1-3 months depending on your college's vacations. At the end of this second internship as well, you fill the worksheet and the attorneys review your work. If the feedback is good after the second internship as well (which is quite common), you get the offer.

This is the ideal way this ideally happens as per the firm's HR. However, the Mumbai office is notoriously known for offering long term round-the-year internships to 3rd-4th year students from local colleges that don't have strict attendance rules, and not making them offers until the time they are taking a break for their final semester exams, and sometimes not then either. Though this is not too common, but there are one or two cases every year where an intern who has been interning with the firm for 1-2 years is told that there are no vacancies in the team right at the time when he/she asks for the offer before going on a break for the final exams.

Also, I don't know how much the approach towards internship evaluation has changed since the pandemic started. I interned there for a couple of months last year (March-April), and when the internship ended, we were told by the HR that our worksheets would be shared with the attorneys for evaluation as soon as the office reopened. Afaik, none of the 8-10 of us got a callback, though some got emails from the attorneys that they had worked with saying that they would recommend the intern for a second internship if he/she was interested to intern again.