It reached 4d on kgs server (account Pachi2 cluster version)
See latest go software updates for the latest update news.
Homepage is at http://pachi.or.cz/.
The source code, written in C, is available at http://repo.or.cz/w/pachi.git.
Windows binaries (include Makefile for MinGW) are downloadable at http://pachi.or.cz/.
The successive versions of the program are named after famous Japanese players:
Pachi 2.00 September 2008 Sana? Pachi 3.00 October 2009 Sanetsu Pachi 4.00 October 2009 Doetsu Pachi 5.00 Februari 2010 Dosaku .... Pachi 8.00 May 2011 Shuhaku Pachi 9.00 October 2011 Hakugen Pachi 10.00 August 2012 Satsugen Pachi 11.00 April 2015 Retsugen
How to use Pachi on Windows (instructions in Russian): http://10kyu.ru/posts/go-bot-pachi-dlya-windows/
You can also check out the derivatives: