Chiron 5.01 released

Chiron 5.01 is a bugfix version: there was a silly bug in the main hash table initialization code that wouldn’t allow sizes larger than 2GB.


Thanks to Lars S., Gabriel P. and Krzysztof G. for reporting and testing.


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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.

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

Chiron wins IGT 2019

Chiron has won the International GSEI Tournament 2019. The tournament was played on October 12-13 in Torino. The playing venue was the sport center La Verdolina. The time control was 30’+10″. Seven rounds were played. Chiron ran on my old server with 2xOpteron 6276 (32 core @ 2.3Hz) except for the game against Dimitri, the runner-up, for which an Amazon EC2 Xeon Platinum 8125M (18 cores @ 3GHz) was used. Like last year, a man vs machine event took place: in the days before the tournament anyone could sign up to play against Marco Belli’s strong Vajolet2 whose search time was limited to 1 second per move. The human who fared better was awarded a plaque. After the end of the tournament Luca Lissandrello tould us he was retiring from computer chess. I would like to thank Luca for everything he has done for the italian computer chess community: he created the G6 forum and website, kept them updated with articles and interviews, organized almost every IGT edition and the IGT online version with a web interface kind of like TCEC, weekly tested new versions of italian engines and surely something else I’m forgetting.

Chiron in the WCCC 2019

From August 11 to 16, Chiron played in the World Computer Chess Championships organized by the International Computer Games Association. The playing venue was the Florence Room 2202 at the Venetian Resort in Macau. Once again the WCCCs took place alongside the International Joint Conference on Artificial Intelligence. During the player meeting, the participants agreed on a double round robin format for all of the three tournaments to play as many games as possible. That meant we had to play every day from 9 AM to 10 PM. On August 11 and 12, the World Chess Software Championship was played. All the participants had to use the same hardware: a notebook with a Pentium Silver N5000. The time control was 45’+15″ for 10 games. Komodo won. Chiron scored 5.5 points, same as the runner-up Jonny but placed third because its SB was lower. On Tuesday 13, the World Computer Chess Championship started. The tc was 90’+15″. For the WCCC and the WSCCC, Chiron ran on an Amazon EC2 instance with two Xeon Platinum 8175M (48 cores) reaching an average speed of 60-70 MNPS in the middlegame and 90-100 in the endgame. EBS storage was used for the 6-men Syzygy bases. Komodo had already won the WCCC after the 9th game. The last one decided the 2nd place. Chiron had to play with white against Komodo having a half a point advantage over Shredder who played as white against Jonny. The Pirc against Komodo ended in a draw and so did the other game thus Chiron was second. Jonny won the Speed Championship (tc 5’+5″). Chiron placed 2nd with 4/8. To be fair, Chiron placement was due also to a lucky book win against Komodo and to Komodo losing one of its games because of connection problems. Congratulations to Komodo and Jonny for their well deserved wins. This was the last edition with Dr. David Levy as ICGA President after 26 years. The handover to the new President, Prof. Jonathan Schaeffer, took place during the dinner on Tuesday 13.
You can find more info about the WCCCs on the ICGA site and on their Facebook page.

Here are some photos:

Chiron in the IGT 2018

During the weekend of October 27-28, Chiron played in the 2018 International GSEI Tournament organized this year by Stefano Gemma. The playing venue was the GAP in Borgo Virgilio, Mantova. Nine progams played a single round-robin. The time control was 25’+10″. Jonny by Johannes Zwanzger won the tournament. Chiron finished second while Pedone by Fabio Gobbato was third after winning the tie-break against The Baron by Richard Pjil. Congratulations to Johannes for a well deserved win. As first of the italians, Chiron is the 2018 Italian Champion. For the first part of tournament, Chiron ran on the same 60 cores Xeon v2 used last year (thanks Wolfgang), and for the remaining games on my 32 cores server with two Opteron 6274, except for the game against The Baron for which an Amazon EC2 instance was used. Jonny ran on a cluster with 384 cores while all the others used local hardware. PICcolino by Luca Naddei runs on a 70 MHz PIC inside a chess board made by Luca himself. Near the end of the tournament a man vs machine match was played: the FIDE Master Valerio Luciani (~2200) played two games against Adachess by Alessandro Iavicoli that won the match. You can find the standings and all the games on GSEI website.

Chiron in the WCCC 2018

From July 13 to 19, Chiron played in the World Computer Chess Championships organized by the ICGA, at the Stockholmsmässan in Stockholm. The hardware for Chiron was provided by the E4 Computer Engineering: a server configured with 2 x AMD Epyc 7551 (64 cores), 256GB of RAM and a very fast Intel Optane P4800X for the Syzygy bases. The average speed was 50/60 MNPS in the middlegame. Chiron placed shared second in the World Computer Speed Chess Championship (12 games, tc 5’+5″). If I had not made it lose a game against Ginkgo by playing a wrong move on the board, it could have been clear second but these things can happen during the blitz tournament. In the World Chess Software Championship all the participants had to use the same hardware: a notebook with an i7-8550U 1.8GHz quad core CPU and 16GB of RAM. The time control was 45’+15″. Chiron scored 4/8 and its only loss was against Jonny after playing the very dubious 16.h3. On Monday 16, the World Computer Chess Championship started. The tc was 1h45’+15″ for 7 games. There was much interest on the WCCC because Leela Chess Zero would have played. Chiron has not a lost a single game but unfortunately has not won one either, thus placed fourth in the WCCC, half a point behind the third. Komodo won all the three championships. Congratulations to its team. The ICML and the IJCAI-ECAI took place in the same days and many partcipants showed interest in our tournaments, following the games, the commentary by GM Harry Schüssler and making questions. This was probably the best computer chess tournament I played in. You could talk with many interesting people from the AI field and some of them also played against our engines, like Prof. Tuomas Sandholm, cocreator of Libratus, who played 4 games against Chiron, almost drawing the last one and thus showing once again I have to work on Chiron’s tendency to trade off all its pieces. Finally, many thanks to the E4 Computer Engineering, in particular to Agnese Reina and Marco Cicala, that let Chiron run on one of their fast servers and prompty solved any technical problem I had.
You can find more info about the WCCCs on the ICGA site and on their Facebook page.

Here are some photos and the games played by Chiron:

Chiron wins IGT 2017

Chiron has won the International GSEI Tournament 2017. The tournament was played on September 23-24 in Rome. Once again, the playing venue was the Accademia Scacchistica Romana. Fourteen programs played 7 rounds. The time control was 30’+10″. Chiron shared the first place with Jonny and then won the tie-break at 5’+5″ by 1.5-0.5. You can find all the results and the games on GSEI’s website. Many thanks to Erdogan Gunes and Wolfgang Zugrav, from Komodo’s Team, for providing the opening book and the very fast hardware Chiron ran on (60 core Xeon v2 @ 2.5GHz). Chiron searched about 60 Mnps in the middlegame and 80 Mnps in the endgame, reaching 100+ a couple of times.

Chiron 4 released

Chiron 4 is about 70 points stronger than Chiron 3.


Here’s a list of the main changes:

  • improved automatic tuning of the evaluation
  • improved evaluation of passed pawns, mobility, opposite bishops endings
  • improved forward pruning in the search
  • improved LazySMP for parallel search
  • support for Windows Processor Groups (more than 64 threads can now be used)
  • NUMA optimization (new UCI and Winboard options “NUMA”)
  • minor speed optimizations
  • fixed a pondering bug
  • fixed two time management bugs under the Winboard protocol

Chiron 4 is available for Windows and Android.
Buyers of the Windows version will also receive a code to get the Android one for free.


Chiron 2/3 Customers can buy Chiron 4 with a discount through the link they have reiceved. Whoever has bought Chiron 3 in the last month will receive Chiron 4 for free.

Chiron wins IGT 2016

Chiron has won the 2016 edition of the International GSEI Tournament. The playing venue should have been at Il Capisterium in Norcia but, because of the earthquake that struck the area, the tournament was held at Accademia Scacchistica Romana in Rome, on September 10-11. There were ten participants, the time control was 30′ + 10″ for 7 rounds. Chiron finished ahead of Booot by half a point. You can read more on GSEI’s website. Thanks to Jeroen Noomen who provided the opening book for Chiron.

Chiron 3.01 released

Chiron 3.01 is a bugfix version.
There was a bug that would often make Chiron crash when Syzygy bases were used.

Thanks to Antonello R. and Christian G. for reporting and helping with testing.