This is the new APM 2.8 autopilot module. The sensors are exactly the same as with APM2. 6, however this version does not have an onboard compass, which makes this version ideal for use with multicopters and rovers.

Does APM 2.6 have internal compass?

The APM 2.6 has no on board compass, and is optimized for vehicles where the compass should be placed as far from power and motor sources as possible to avoid magnetic interference. APM 2.6 is designed to be used with the 3DR GPS uBlox LEA-6 with Compass module.

Does Pixhawk have internal compass?

The internal compass may be useful on larger vehicles (e.g. VTOL) where it is possible to reduce electromagnetic interference by mounting the Pixhawk a long way from power supply lines. On small vehicles an external compass is almost always required.