It is a WebP file, a modern image format developed by Google that provides superior lossy and lossless compression.
Many users find this "interesting" or frustrating because when they try to save images from Reddit, they receive a .webp file instead of a standard JPEG. This happens because: w3cpmezh0rp91.webp
Reddit often serves images in .webp format to save bandwidth and improve loading speeds, even if the user originally uploaded a .jpg or .png . Why are you seeing a .webp ? It is a WebP file, a modern image
Reddit's UI automatically converts images to WebP to reduce file sizes by roughly 25-35%. It is a WebP file