According to the cover note of Full Metal Panic! Sigma
vol.15, a spin-off novel of Full Metal Panic!
was announced to be released by Fujimishobo. It's a sequel taking place ten‐odd years after the finale of the original novel. A newface author Ohguro Naoto will write it under the supervision of Gatoh Shoji
Key illustration of the spin-off novel
Gatoh will release a new collection of short stories as announced before.
Source: Scan of the cover note