Chiron 5 released

On June 21 of eighteen years ago, Chiron played its first over-the-board tournament, the 2003 Italian Computer Chess Championship (CIPS), where it placed fifth, thus today it felt a nice day to release its fifth version.


Chiron 5 is about 110/120 points stronger than Chiron 4. Most of the gains come from improvements in search and move ordering but also the evaluation has been improved and tuned by playing several million games.


Here’s a list of the other main changes:

  • support for 7-men Syzygy Bases
  • improved time allocation
  • KPPKP Chiron Bitbase integrated in the executables
  • support for Arena (.abk) opening books (thanks to Graham O’Neill for the specs). The params saved in the book are used to choose the moves
  • a second opening book can be used
  • Elo limits have been retuned
  • cpu/core count now works correctly on systems with more than two sockets (thanks to CoffeeOne)
  • some other minor bug fixes
  • new benchmark

Chiron 5 is available for Windows. The Android version will be released in the next weeks and will be free for Windows customers. Once released, they will receive a code to get it. UPDATE JULY 17: Chiron 5 for Android has been released. All the emails with promo codes have been sent to Chiron 5 customers. If you have not received it, please contact


As always, past customers can buy Chiron 5 with a discount through the link they have received.


There is for now a significative gap with NNUE engines but if, nevertheless, you are considering getting Chiron to support its development, thank you.

Several emails have bounced back because the addresses are no longer valid. If you have not received it, please contact


If your copy is not dated 25 June, please download it again from the same link you received.