Question: is surface pro 3 pen compatible with surface pro 4

Answer: Yes, A new version of the Surface Pen was launched in 2014 with the Surface Pro 3. Based on technology developed by N-trig (a separate company at the time, though subsequently acquired by Microsoft), the Surface Pro 3 version lacks the eraser tip present in the previous generation; erasing is done by drawing over the ink strokes while holding down one of two physical buttons on the side, above the button used for right-clicking. A third button, located in place of the eraser tip, sends a Bluetooth signal to a paired Surface PC which instantly opens OneNote, even when the device is locked (although advanced editing functions are disabled in this case). Unlike the Wacom-powered Surface Pen, it requires two batteries: one AAAA battery for stylus operation, and two size 319 coin cell batteries for the top button. The pen is included with all Surface Pro 3s but is also compatible with and available as an optional accessory for the Surface 3. It is also compatible with all subsequent Surface PCs, which uses the same basic technology. Surface Pro 3 Pen is able to detect 256 levels of pressure on its tip.