Engine Room : Special Fat Edition

Sherwood, Russell  Tuesday, February 16, 2021

Disclaimer: Any opinions given are my own and not necessarily representative of any group or body I am associated with.

I had intended to give a run down on the latest in Engine development but instead, based on the number of contacts I have had over the weekend, will focus on one – Fat Fritz 2

Fat Fritz 2 was recently released in a swathe of advertising by Chessbase. They claimed this engine was the new number 1 and so on……https://en.chessbase.com/post/fat-fritz-2-best-of-both-worlds

Without going into detail, this release caused great consternation within the Stockfish and wider engine development community, over copyleft (yes left – look it up!), naming, charges and claims.

I will not go into much depth on the Copyleft issue but in simple terms, under the Stockfish GPL License the full code, including the network if embedded, has to be published. Initially the engine was published without the network, then with a different network to that being sold. 

Whilst this may or may not be still breaking the rules, it is still causing some major arguments.  In the defence of Chessbase  there are several other Stockfish variants which refuse to publish source code – Eman, Zeus, AI and Killifish come to mind, although the key difference is that none of these engines are Commerical

The reality is that the original part of Fat Fritz 2 is a larger network and (less originally) that this network is based on Neural Net Evaluations rather than Stockfish. From this, the issue caused is that the engine should be really called Stockfish + Fat Fritz 2 Network.


Putting all this aside (We are here to play Correspondence Chess after all) – how strong is Fat Fritz 2 and is it worth buying?

Chessbase claim this is the new number 1 – having beaten Stockfish 12 is a match. There are a number of issues with this claim……

  1. The match size was tiny – to prove actual decisive superiority requires a much larger match with hundreds or preferably thousands of games involved.
  2. Stockfish 12 was used , whereas FF2 is based on a Stockfish Dev(1). This would mean that the engine, ignoring the network, would be around 30 elo stronger. In practice, we are comparing apples with oranges!

This means that the results of the match are inconclusive and not really indicative of a clear new number 1.  Independent testing has shown that FF2 is around the same strength as Stockfish rather than being any stronger. For example https://www.sp-cc.de/

To complicate matters there are two versions of Fat Fritz – The Commercial Version and the Stockfish Github Version. The network released with the Free version is around 45 elo weaker than the commercial one.

Practically the Correspondence player is not really interested in the results of those matches as they are played at, for us, very rapid time controls. I undertook some soft testing of the Free version over the weekend – running it on a few threads alongside my main engine. Most of the time it suggested the same moves but on occasion it did provide some interesting alternatives. 

It is worth commenting that the similar results are  seen if Stockfish and LC0 are run in parallel.

Looking from a wider perspective: Is this engine likely to be stronger for Correspondence Chess. I suspect the answer is yes, as the more knowledge embedded in the network, the better the overall moves should be. The same is true for LC0 networks – a well-trained large network should give better suggestions than a smaller well-trained network, if time is not a factor.

Is it worth the money – my gut feel is if, you want an edge for 1-2 month and consider 80 euros a reasonable price then yes, otherwise use the Free version (WCCF members get in touch if you want a copy) to generate ideas and alternative lines.

Over the next few months, I would expect that:

  1. Unless Chessbase release regular updates, FF2 will become weaker than Stockfish.
  2. New networks, based on either the CB Network, Free Network or developed from scratch will appear., which will be stronger than the FF2 Commercial network.
  3. Other network structures for NNUE will be developed which may eclipse the current standard or FF2 structures.

Of course Ceres may also upset this apple cart but more on that next time.

(1)As a reminder Stockfish do a major release every so often – For example Stockfish 11 and Stockfish 12. In between these major releases minor improvements are released, almost daily. These minor releases (Stockfish Dev) tend to add an elo or two to Stockfish at a time. When enough of an overall gain is made, a new Major release is made





Engine RoomEnginesFat Fritz2

Updated Tuesday, February 16, 2021 by Russell Sherwood

Welsh Correspondence Chess FederationBritish Correspondence Chess AssociationClergy Correspondence Chess ClubSchemingMind Internet Correspondence Chess ClubSocial Correspondence Chess AssociationNational Correspondence Chess ClubWelsh Chess UnionInternational Correspondence Chess Association