Cross-post from BRF, originally posted by Pit.

Russia develops K-100-1 for Su-35
Reuben F Johnson JDW Correspondent
Jane’s Defence Weekly – July 11, 2007

Officials from Agat Research Institute, which is developing the seeker, confirmed that the K-100-1 is the KS-172 relabelled and that the missile has a large diameter (350 mm) Agat seeker — a variant of the 9B-1103M seeker originally developed for an active-homing version of the R-27 AAM.

“We refer to this seeker design as the ‘shayba’ [Russian for ‘hockey puck’] when we are talking about it at the design bureau because it is wide and squat in its shape compared to the rest of the 9B-1103M derivatives,” an Agat technician said.

“The lock-on range for the seeker is 40 km, but this is of course one fifth or less than the overall range of the missile,” said one designer.