I wrote:
The upcoming GNU Go 3.6 release will be able to resign games. (This is already included in the latest development version 3.5.10.)
It would of course be nice if as many GTP clients as possible would support this feature by the time it gets released.
Marco Scheurer wrote (on gnugo-devel):
Following Arend's request about support for resignation in clients on the GTP mailing list I just remembered that Goban has had in fact built-in support for resignation for quite some time... Is there a quick test to make GNU Go resign? I've been trying 9x9 with 9 handicap stones, and it passes after a few moves.
Resignation is only enabled on 19x19 (on the basis that small board games are fast enough not to get boring anyway). Try resuming the attached game, play a white move at E9, and GNU Go 3.5.10 will resign as black.
Arend