CCC PGN IV

In the previous post on engine vs. engine tournaments, TCEC S21 L4 Underway; CCC Opening 'Specials' (May 2021), I wrote,

After the three [CCC] events titled 'Eco Mini-Match', the site launched into a series of events based on specific openings. The first was 'Caro-Kann Special' with four engines -- Stockfish, Lc0, Dragon, Stockfish Classic (finishing in that order) -- in a round robin of 30 game mini-matches using a blitz time control. [...] At some point in my long, undistinguished chess career, I've played all five openings that have been explored to date. It might be useful to examine the results, but first I have to locate the PGN for the five events.

Locating the PGN turned out to be fairly trivial. Here is the sequence I used for 'Sicilian Najdorf Special':-

1. Switch to the event to be downloaded (using the inverted triangle to the right of the current event name)
2. Select the 'PGN download' icon to the right of the game displayed.
3. Select the 'Event' tab.
4. Click the 'PGN download' icon.

On that last step, I received no feedback that anything had happened, but the file was indeed downloaded to my usual target directory. I opened it with SCID and discovered that it contained 300 games, all starting with the moves 1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6. SCID reported the frequency of sixth moves by White as shown in the following chart.

Since the moves most played are currently the most popular for human players, I suspect that the engines are being guided by humans. The PGN for the first game in the file showed 'book' through White's sixth move (6.h4). The last game in the file showed 'book' through White's 16th move. Ugh! It would be far more interesting to let the engines play the variations without being guided at every step by players who might have ratings 1500 points less than the engines. (The 'Info' tab for the Najdorf event indicates the engines' average rating is around 3500).

The last time I looked at the topic of this post was CCC PGN III (September 2020). The CCC appears to have standardized its method of making PGN files available, which is certainly a welcome development. The Najdorf 'Info' tab points to the same 'Mystery Engine' PGN that I mentioned in Stockfish Wins TCEC Cup 7; CCC GPUs Back (November 2020). The current method for accessing CCC PGN files might go back at least that far.