According to e-hon bookstore, the new volume of Full Metal Panic! novel was announced to be released on July 17th. The title is "Zutto Stand by Me Part 1 (of 2 or 3)", indicating there will be one or two more volumes. The author Gatoh Shoji revealed in the afterword of the last volume "Semaru Nick of Time" (2008) that the main story will be concluded by the next volume and the release date had been the center of Full Metal Panic fans' attention. On January 5th, Gatoh posted in his blog that the final volume might be released this Spring but he withdrew the comment on May 14th.

Source: e-hon, Gatoh's official blog

Updated on May 21st
Gatoh posted in his blog that the part 2 of 2 of the volume 11 will be published soon.

Updated on May 25th
According to Fujimishobo's notice to the bookstores, the final volume will be released this August.

Source: Scan of the notice