I picked up a few of these sidemount NeoPixels(SK6812 based) from Adafruit this week. It almost looks like a Particle logo on that die? 
The casing of the LED is 3.9 x 1.9 mm (0.153543 x 0.0748031 inch). Very convenient part that I’ve been wanting for quite some time. Perfect for lighting up a PCB to show the user where to put an NFC card and such. With 1.9mm height, you can use 2mm acrylic for diffusion. Looking forward to put this on a board!
