The Pentax K mount extension tubes work with full aperture metering, the TTL meter itself takes into account any effects of the additional extension, the mechanical linkage (not aperture actuation pin) takes care of the relative apertures as the lens is set to for the actual exposure.

The F and ESII cameras and SMC Takumar full aperture lenses use similar mechanisms to the K mount bodies & lenses but with the M42 mount and there was a matching set of extension tubes.