It’s now possible to transfer Marriott points to Starbucks Stars at a rate of 1,000 Marriott : 100 Starbucks stars. Marriott isn’t the most valuable currency, but Starbucks is even worse when you consider this transfer rate.
As a reminder Starbucks stars can be redeemed for the following:
25 Stars: Customize your drink
100 Stars: Brewed hot or iced coffee or tea, bakery item, packaged snack, and more
200 Stars: Handcrafted drink (Cold Brew, lattes, and more) or hot breakfast
300 Stars: Sandwich, protein box, or at-home coffee
400 Stars: Select Starbucks merchandise
I don’t think transferring makes sense unless you have a small amount of Marriott points and don’t plan to use the program in the future.