According to specifications found in the internet, this lens has SDM autofocus only. The K-10D originally did not support SDM, but this was not caused by hardware. After Pentax itself sold such lenses, they offered a firmware update for the K-10D (V1.30). With this, the lens should work alright. However, I own neither a K-10D nor that Sigma lens, so better wait for more comments.
EDIT
Reference for the lens specs (SDM only):
http://www.dpreview.com/lensreviews/sigma_18-250_3p5-6p3_os_c16
Reference for the K-10D (V1.30): The camera database of this forum