Niantic have released the famous Golden Magikarp and the shiny Red Gyarados into the wild.
Trainers across the globe have reported sightings of golden Magikarp in the wild. These Shiny Magikarp are extremely rare, so pay close attention to the Magikarp you encounter while you’re out exploring the world to make sure you don’t miss the opportunity to catch one!
The post states that they will be "extremely rare" to find. What are the chances the Magikarp is a shiny?