TCEC Season 20 Further information

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This is a temporary version!! The page below is not yet final.

TCEC Season 20 - Further information - this TCEC Season 20 page is a supplement to TCEC Season 20 Rules

Special rulings

...(no exceptional cases yet)

Further information

Engine Specific Configuration

UCI and Xboard (Winboard) engines are supported. To identify the protocol an engine is using you can hover over the king figure placed above the engine logo during a game. This info will be saved for the archive, but does not work for Season 5 or older games.


Many engines come with different executable files. 64-bit executables are always preferred over 32-bit. Also, compiles that support SSE 4.2, AVX/AVX2 or similar instruction sets are preferred. An author can also submit an script that is then used to download/clone and compile the engine. Not stripping the optimized executable of debugging information is recommended.

Large Pages

Large pages are automatically in use, nothing needs to be done by engines.

Number of Cores / Threads

Each engine can use up to 176 cores of the processors, if this is supported. Some engines have a prefix like "deep", but this has been omitted from the engine name to make it shorter. When watching a game you can see the number of cores that are in use by hovering over the king figure above the engine logos.

Split Depth

The split depth parameter basically defines the minimum depth for work to be split between threads. If no specific settings are given from the programmer, the default value will be used.

Main Hash Size

Each engine is allowed to use up to 128GiB of hash but 64GiB maximum is recommended. Not all engines support this much hash, so the maximum for that engine will be used in this case, typically 2 GiB or 8 GiB MB. The author's preference for Hash size is always used up to the 128GiB limit. When watching a game you can see the size of the hash that is in use for the engines currently playing by clicking the gears next to the engine logo.

Minor Hash Sizes

Some engines have an option to configure the size of other hash tables, often called pawn hash or evaluation hash. The combined, total limit for hash types like these is 256 GiB.

Own Opening Book

All opening books shipped with the engines are removed and/or disabled and any engine found to be using hidden, internal opening books will be disqualified and replaced with another engine chosen by the Tournament Director.

Endgame Tablebases

For all divisions, 5-men Nalimov/Gaviota/Scorpio, and 6-men Syzygy are available and cached in RAM if enough free RAM is available. When watching a game you can see the type of the tablebases (if any) that is in use for the engines currently playing by clicking the gears next to the engine logo.

Ponder / Permanent Brain

Basically this means that the engines can think during their opponents turn. It is not allowed so it will be disabled because of performance limitations with only 1 computer. This might change in a future Season of TCEC.

Contempt / Draw Score

Some engines have a setting that can adjust their own view of the positions throughout a game to avoid draws. This setting is not changed from the default unless it is a request from the programmer.

Other Settings

Any configurable option not described above, is not normally adjusted in any way, except if the programmer of an engine wants specific settings for each specific Division. :Options like "keep hash tables" or similar is usually enabled.

TCEC Hardware

Thanks to our devoted audience for it's support in the form of donations, subscriptions and cheers!
Special thanks to noobpwnftw who sponsors TCEC with the current playing hardware mentioned hereafter!

Current TCEC CPU server

  • CPUs: 4 x Intel Xeon 4xE5-4669v4
  • Cores: 88 physical / 176 threads
  • RAM: 128 GB DDR4 (available to engines)
  • RAM: 1 TB (available to 6-pieces Syzygy)
  • HDD: 7 TB total
  • OS: CentOS Linux release 7.7.1908 (Core)

Current TCEC GPU server

  • GPUs: 4x V100
  • CPU: Intel(R) Xeon(R) Platinum 8163 CPU @ 2.50GHz, 32 vcores
  • RAM: 48GiB (available to engines)
  • RAM 128GiB (RAM unused by engines is used for caching tablebase files)
  • SSD: 500GB
  • 6-piece Syzygy and 6-piece Scorpio bitbases
  • OS: Ubuntu 18.04.4 LTS


Is this the official World Computer Chess Championship?

No, it is not, although many people regard it as such.

Who is the reigning TCEC Grand Champion?

Stockfish defeated LCZero in the Superfinal of Season 18, so Stockfish is the reigning TCEC Grand Champion.

Who is the winner of the TCEC Cup?

Alliestein won the TCEC Cup in a final match with LCZero. Stockfish came in third and Fire made it to fourth place.

Did the engine move instantly?

Yes, some engines can move from hash, or move instantly (instamove of 0 seconds). However, sometimes it can seem that it moves instantly but in reality it doesn't, since there is a transmission delay from the playing server to the website. Refer to the "move time" for each engine to see how long it thought on its move.

Is there a special plugin required to view the games?

No, to view the games it is only required that you allow Javascript to run. The TCEC Web GUI has been developed by Octopoulo, improving on the ideas of Ben Reese and Arun Sathya. It will run on the latest Chrome, but also on the latest Firefox. There is no support for Internet Explorer versions below 9.

What are you using to play the games?

To play the games a special version of cutechess-cli is used. This is a command line tool without an actual GUI. This was made possible thanks to Jeremy Bernstein and Arun Sathya. Previously TCEC used ChessGUI by Matthias Gemuh.

Who are the authors of the GUI?

The current web GUI has been developed and created from scratch by Octopoulo, building on the ideas behind the older one created by Ben Reese and Arun Sathya. Previous seasons used a GUI by Martin Thoresen, currently known as legacy GUI.
As of Season 17 the new TCEC Official GitHub will be used for further development.

What is the name of the web framework that displays the games?

For the current web GUI it is chessboard.js and cutechess-cli. For the legacy GUI and archive GUI it is called pgn4web and is totally free. Paolo Casaschi is the mastermind behind it and has helped a lot on certain difficult programming challenges.

Who is the author of the opening books used?

The author of the Superfinal opening book (Book E) is Jeroen Noomen (aka Jeroen_TCEC); the author of all other opening books (Book A-D) used during TCEC tournament games is Nelson Hernandez (aka CatoTheYounger_TCEC).