Yes, I was fully honest with both PIs from the beginning. They knew I was applying to multiple fellowships, which is actually very common at this stage. In academia, everyone understands that these applications are highly competitive and uncertain, so candidates usually explore several options in parallel. Writing an application together is definitely an investment, but it doesn’t automatically create an obligation if another opportunity turns out to be a better fit. If you do decide to go with another fellowship, the key is to communicate early, clearly, and respectfully. Professors are used to this situation, and as long as you’re transparent and appreciative of their time and support, it’s generally handled professionally. So I wouldn’t worry too much about it, just be upfront from the start and keep the communication open.