For the sake of easy reference, I'll leave the relevant snippet from the linked article so people can decide for themselves with a bit more information:
> Another important note - some binary blobs and other non-free software components are used today in PebbleOS and the Pebble mobile app (ex: the heart rate sensor on PT2 , Memfault library, and others). Optional non-free web services, like Wispr-flow API speech recognizer, are also used. These non-free software components are not required - you can compile and run Pebble watch software without them. This will always be the case. More non-free software components may appear in our software in the future. The core Pebble watch software stack (everything you need to use your Pebble watch) will always be open source.
> Another important note - some binary blobs and other non-free software components are used today in PebbleOS and the Pebble mobile app (ex: the heart rate sensor on PT2 , Memfault library, and others). Optional non-free web services, like Wispr-flow API speech recognizer, are also used. These non-free software components are not required - you can compile and run Pebble watch software without them. This will always be the case. More non-free software components may appear in our software in the future. The core Pebble watch software stack (everything you need to use your Pebble watch) will always be open source.