What chess engine does this game use? Is it Stockfish?

[MineralsMan]

What chess engine does this game use? Is it Stockfish?

[Ziggy]

Not much information out there on this topic. The developers have stated that Grandmaster plays at 2400/2500 strength, which is quite low. At time of release Stockfish would have been in version 8 I believe? That's about 1000 Elo over Chess Ultra so unlikely it's using Stockfish. Additionally, even though Stockfish is open source I think the developers would still have had to give credit if being used or modified.

In short, we don't know but I suspect it's an in-house engine. Also unknown what, if any, endgame tables it uses and likewise, its opening book remains a mystery.

[MineralsMan]

Interesting interesting. I've looked at their other games, it doesn't look like this is a chess-dev company. Would be so weird if they managed to develop their own engine that quick :thinking: I wonder if they've licensed an engine. I hear Fritz licenses the older versions to game devs?

[Ziggy]

Many developers and independents developing chess engines. In this case Ripstone put out Pure Chess in 2016 and Chess Ultra in 2017 so not inconceivable that they created their own engine. I have used many iterations of Fritz and the oldest version I've matched against CU was Fritz 13 (from 2011), which won the game. Has a rating of around 2950, which is not bad for a single core engine. The latest, Frtiz 17 (running on 6 cores), destroyed CU with ease. No surprise given its rating of 3300. Although Fritz is now lagging somewhat behind the likes of Stockfish and Komodo it is still (and has been) a strong engine so I doubt this is the framework for CU.

If Ripstone have licensed or modified an existing engine it would require credit to be given, I believe so it all leaves us in the dark.

If you do find out anymore, please post because I'd be very interested to hear about it.

I've copied the PGN for the Frtiz 17 vs CU game below, if you want to see how it played out. If you don't have a chess GUI you can copy / paste using Chess.com or Lichess online.

[Event "?"]
[Site "?"]
Dec 31, 1969 @ 4:00pm[Round "?"] [White "Fritz 17"] [Black "Chess Ultra"] [Result "1-0"] [ECO "A07"] [PlyCount "93"] 1. Nf3 Nf6 2. g3 d5 3. Bg2 c6 4. O-O Bf5 5. d3 e6 6. Nbd2 Nbd7 7. Qe1 Nc5 8. Nh4 h6 9. b4 Na4 10. Nxf5 exf5 11. Rb1 Bd6 12. Nf3 O-O 13. Nd4 f4 14. Bxf4 Bxf4 15. gxf4 Qc7 16. Qd2 Rad8 17. e3 c5 18. bxc5 Nxc5 19. Qc3 Qc8 20. a4 a6 21. Rb6 Rfe8 22. Rfb1 h5 23. a5 h4 24. h3 Nfd7 25. Nf5 Ne6 26. Qxc8 Rxc8 27. Rxb7 Ndc5 28. R7b6 Nb3 29. cxb3 Rc5 30. Nd6 Rf8 31. b4 Rc3 32. Bxd5 Rxd3 33. Bc4 Rc3 34. Rxa6 Rb8 35. b5 g6 36. b6 Nd8 37. Ra7 Kh8 38. a6 Nc6 39. Rc7 g5 40. Rxc6 Rg8 41. Nf5 Ra8 42. b7 Rc1+ 43. Rxc1 Rf8 44. Bxf7 Rxf7 45. b8=Q+ Rf8 46. Qxf8+ Kh7 47. Qg7# 1-0
[Round "?"]
[White "Fritz 17"]
[Black "Chess Ultra"]
[Result "1-0"]
[ECO "A07"]
[PlyCount "93"]

1. Nf3 Nf6 2. g3 d5 3. Bg2 c6 4. O-O Bf5 5. d3 e6 6. Nbd2 Nbd7 7. Qe1 Nc5 8.
Nh4 h6 9. b4 Na4 10. Nxf5 exf5 11. Rb1 Bd6 12. Nf3 O-O 13. Nd4 f4 14. Bxf4 Bxf4
15. gxf4 Qc7 16. Qd2 Rad8 17. e3 c5 18. bxc5 Nxc5 19. Qc3 Qc8 20. a4 a6 21. Rb6
Rfe8 22. Rfb1 h5 23. a5 h4 24. h3 Nfd7 25. Nf5 Ne6 26. Qxc8 Rxc8 27. Rxb7 Ndc5
28. R7b6 Nb3 29. cxb3 Rc5 30. Nd6 Rf8 31. b4 Rc3 32. Bxd5 Rxd3 33. Bc4 Rc3 34.
Rxa6 Rb8 35. b5 g6 36. b6 Nd8 37. Ra7 Kh8 38. a6 Nc6 39. Rc7 g5 40. Rxc6 Rg8
41. Nf5 Ra8 42. b7 Rc1+ 43. Rxc1 Rf8 44. Bxf7 Rxf7 45. b8=Q+ Rf8 46. Qxf8+ Kh7
47. Qg7# 1-0

[JediMasterStef]

Originally posted by Ziggy:

Not much information out there on this topic. The developers have stated that Grandmaster plays at 2400/2500 strength, which is quite low. At time of release Stockfish would have been in version 8 I believe? That's about 1000 Elo over Chess Ultra so unlikely it's using Stockfish. Additionally, even though Stockfish is open source I think the developers would still have had to give credit if being used or modified.

In short, we don't know but I suspect it's an in-house engine. Also unknown what, if any, endgame tables it uses and likewise, its opening book remains a mystery.

I don't think rating has much to do with the engine used.
Chess Ultra's AI has 10 different difficulty settings. That doesn't mean it has 10 different engines, but 10 toned down versions of the same engine.

Here is a quote from Simply Chess (another chess game on steam):
"Play against the computer – World class "Stockfish" AI with 100 difficulty levels."

You can indeed make a low rated AI using Stockfish.

[Ziggy]

Umm yes, I do get that engines can play at lower strength. No one has actually said otherwise. Your argument then begs another question; if it was using Stockfish (or any other engine) why cripple it? Wouldn't it make more sense to have Grandmaster play at full strength and scale from there?

This is the standard model employed by every other chess program I can think of, or have used. The difficulty is simply one of many adjustable parameters for a chess engine, such as Stockfish. There is absolutely no need for a separate engine. I have Stockfish (and several others) installed in the Fritz GUI. You tell it where the main binary is located, set the initial parameters and it builds a UCI (universal chess engine) file and that's it. It doesn't spam modified copies of the binary exe. Here's the contents of my Stockfish UCI file:

Name=Stockfish 12
Author=the Stockfish developers (see AUTHORS file)
Filename=C:\Program Files (x86)\Common Files/ChessBase/Engines.uci/Stockfish 12\stockfish_20090216_x64_bmi2.exe
Priority=below normal
[OPTIONS]
UCI_Chess960=true
Threads=6

You can see I've told it to use 6 cores by default but I don't need a 6-core specific engine (or version). It can handle whatever you want, provided the cores are there.

[JediMasterStef]

I quote again what you said earlier:

Originally posted by Ziggy:

(...) The developers have stated that Grandmaster plays at 2400/2500 strength, which is quite low. At time of release Stockfish would have been in version 8 I believe? That's about 1000 Elo over Chess Ultra so unlikely it's using Stockfish. (...)

If engines can play at lower strength how can we conclude it's not Stockfish?

The rating of a regular human grandmaster is around 2500, so the grandmaster AI corresponds to that.
What is the point of playing against an uncrippled Stockfish? It has a rating of 3500, no human can beat it.

[Ziggy]

I'm sorry but just not following your reasoning here. How many CU users do you think are GM level? The vast majority of players, myself included, don't stand a chance of beating the engine at 2400/2500 so by your 'logic' why not set GM difficulty even lower?

If you bought a Ferrari, without access to a race track, would you demand it be speed limited?

As to the point of playing against a 3500 opponent, how about as a training tool and for analysis? There are many benefits to playing against or employing a strong engine as a kibitzer. At my level, I can't hope to beat CU on Grandmaster but there will be folks out there who can so why not give them the option for more of a challenge? It doesn't hurt lower rated players.

Having an 'uncrippled' engine means that everyone, regardless of skill level can play against an opponent that suits them. or, as you suggest, the devs deliberately chose an arbitrary cap which to me is odd, in comparison to other chess programs.

Look, you seem utterly convinced and determined to persuade us that CU is Stockfish. I'm doubtful, that's all, so we'll just have to disagree on this. I don't particularly care either way. However, proceeding to school us noobs with your big revelation that engines can play with variable strength (wow, really?) doesn't exactly steer us towards friendly discussion.

There is no mention of third party developers or engine in the game credits which is what really leads me to the simpler conclusion that the engine is in-house. If I'm wrong, so be it, and I'll be interested to know more, as I've already said in an earlier post.

[JediMasterStef]

Originally posted by Ziggy:

I'm sorry but just not following your reasoning here. How many CU users do you think are GM level? The vast majority of players, myself included, don't stand a chance of beating the engine at 2400/2500 so by your 'logic' why not set GM difficulty even lower?

If you bought a Ferrari, without access to a race track, would you demand it be speed limited?

As to the point of playing against a 3500 opponent, how about as a training tool and for analysis? There are many benefits to playing against or employing a strong engine as a kibitzer. At my level, I can't hope to beat CU on Grandmaster but there will be folks out there who can so why not give them the option for more of a challenge? It doesn't hurt lower rated players.

Having an 'uncrippled' engine means that everyone, regardless of skill level can play against an opponent that suits them. or, as you suggest, the devs deliberately chose an arbitrary cap which to me is odd, in comparison to other chess programs.

Look, you seem utterly convinced and determined to persuade us that CU is Stockfish. I'm doubtful, that's all, so we'll just have to disagree on this. I don't particularly care either way. However proceeding to school us noobs with your big revelation that engines can play at variable strength (wow, really?) doesn't exactly steer us towards friendly discussion.

There is no mention of third party developers or engine in the game credits which is what really leads me to the simpler conclusion that the engine is in-house. If I'm wrong, so be it, and I'll be interested to know more, as I've already said in an earlier post.

I only claim the strength of the AI is no proof the engine used is not Stockfish. That's it, everything else is you putting words into my mouth and ranting about developer decisions.

[Ziggy]

Ranting about developer decisions? Are we reading in the same thread here? I clearly stated it would be ODD if they opted for an arbitrary cap. As in out of the ordinary, not the norm, unusual. It certainly wouldn't upset me if that was the case. I made no claims to presenting 'proof' either, in any of my posts. Sorry if sharing my own thoughts and reasoning (for discussion) bothers you but this could have been a very interesting thread (and do I enjoy hearing the thoughts of others) without turning it into a confrontation. Allow me to be frank, it's YOUR smart *ss attitude that irked me, not the developers.

[MineralsMan]

hmmmm So I checked the local files and there is no copy of the Stockfish license or source code. I read their license and any game that uses it must include a copy of the source code and license that the user can access. I believe this is the same for all open source engines. So my theory is that it is not an open source engine.

I just checked my local files for another chess game I have on steam: Check vs Mate. It also has no source codes. But it's store page does say it is using a version of the Fritz engine! So a license of Fritz does not require the sharing of the engine in local files.

Here we see that it uses Fritz 10 ... a much older version even though the game is much newer than fritz 10's release date. So maybe Chessbase only licenses old old versions of Fritz so other products can't compete with them: https://en.wikipedia.org/wiki/Battle_vs._Chess

Like CU, CvM has 10 difficulty levels :thinking:

[MineralsMan]

ok, after reading this, I'm almost certain they didn't make their own engine:

https://www.unrealengine.com/en-US/developer-interviews/ripstone-discusses-the-impact-of-ue4-on-the-development-of-chess-ultra?sessionInvalidated=true

3 devs (1 of whom was an intern) with apparently 0 chess-software experience and a tight deadline :thinking: the plot thickens

[Ziggy]

Could be on to something there. Note that the engines don't necessarily have discrete difficulty levels (though the GUI front end may have canned settings), contrary to some misinformation posted earlier. Behind the scenes, there are many configurable parameters within a chess engine which will affect the overall playing strength. In addition to those you have generic 'external' factors such as book knowledge / learning, pondering, hash tables, endgame tables and so on.

Here's the interesting thing though; the handicap mode of Fritz 10 had an adjustable Elo rating of 1375 to 2337 (though the engine could play around 2780 full strength). Thinking 2337 with CU GM around 2400 ... hmmm.

So Fritz 10 could be a potential candidate. I'm no expert on intellectual property / copyright but I would have thought Ripstone would be required to credit Chessbase / Fritz? The Fritz engine has different developers after version 13 and I'm not even sure who the licensing rights now belong to for older versions.

Keep up the detective work and keep us posted!

[MineralsMan]

Nice. I did not know F10 had a nearly identical playing strength. That all but confirms it's F10 ... 1 final "aha" ---> Read through the various engines and check out which is the only one that works on various game consoles: https://www.chess.com/terms/chess-engine#fritz

I think that's it's gotta be it!

[Ziggy]

You have got me leaning towards Fritz v? as a contender but other engines could work on consoles. The engines in the list are all UCI engines, with the notable exception of AlphaZero, designed for supercomputing. Fritz just happens to be the engine of choice. No surprise since the console software the article is referring to is by ... you guessed it, Chessbase. Makes sense that they'd employ their own engine. Stockfish is a favourite on mobile apps, to give another example, but I'm also running Shredder on iPhone.

To be honest, it's the whole licensing issue that has me puzzled, or lack thereof in the credits. I have no idea what kind of deal Ripstone might have cut with a third party developer and I suspect we'll never know for sure.

[MineralsMan]

:thinking: true true. So odd that they'd not mention the engine at all ... even if they made their own, you'd think they'd mention making one.