User:Banedon/sandbox2

The 15th season of the Top Chess Engine Championship began on the 6 March 2019. It is currently ongoing.

The season featured for the first time two separate Division 4s, the winners of which moved to a playoff for promotion to Division 3. Also notable is the emergence of a new neural network based engine based on AlphaZero, AllieStein, which reached the premier division.

Structure
The season comprised six divisions: two Division 4s (4a and 4b), a Division 3, 2, and 1, and the Premier Division. The top two engines of Division 4 advance to a playoff against each other, with the top two finishers advancing to Division 3. From there on, the structure is the same as the previous seasons: the top two engines of each division promote to the division above, while the bottom two engines relegate. The top two engines of the Premier Division contest a 100-game superfinal. The lengths of the opening books used increases as the divisions progress. The time control increases from 30 minutes + 5 seconds per move in Division 4 to 90 minutes + 5 seconds per move in the Premier Division.

Rules
After the controversial game 66 in the previous season's superfinal, TCEC modified its rules for disconnects: in most situations, instead of a restart from scratch, the games will be resumed from the last available position, albeit with time compensation for both engines to fill up their hash tables. The only other significant change is to remove the number of Black wins from the tiebreak criteria, leaving the tiebreakers as 1) number of crashes; 2) Direct encounter; 3) number of wins; 4) Sonneborn–Berger score; 5) tournament director decision. Beyond that, the season used the standard rules of the TCEC.

Division 4a
Nemorino, which had been relegated in Season 14, convincingly won Division 4a. It scored 13 wins in 18 games, and conceded only one loss, to finish 2.5 points ahead of the next-nearest competitor. Second place was more hotly contested. RubiChess defeated Winter head-to-head twice, but also lost both games to Nemorino. Winter scored more wins overall, but ultimately the head-to-head tiebreak meant RubiChess qualified for the playoffs.

Division 4b
In contrast to Nemorino's dominating performance in the other division, Pirarucu won Division 4b by only half a point, just ahead of AllieStien, who was in turn only half a point ahead of Wasp. Pirarucu lost the head-to-head against AllieStein, but also managed to dominate the lower half of the field harder than AllieStein. ScorpioNN, which had been thoroughly outclassed in the previous season's Division 4, showed it had improved tremendously to finish mid-table with 5 wins and 5 losses.

Playoffs
Nemorino, RubiChess, Pirarucu and Alliestein qualified for the playoffs. In a dominating performance that showed how fast it was improving, AllieStein crushed the field and finished 3.5 points above second-placed Nemorino, winning all four of the head-to-head games against Nemorino and losing only one game to RubiChess. Despite the losses to AllieStein, Nemorino finished 1.5 points ahead of third-placed Pirarucu on the back of two head-to-head wins.

Division 3
Division 3 was closely-contested, with every engine winning and losing games. rofChade and Alliestein finished first and second with 18/28 and 16.5/28 respectively, ahead of third-placed Arasan with 15.5/28. Arasan had missed out on promotion in Season 14 because eventual Premier Division engines Komodo MCTS and Leela Chess Zero were also in the division, and finished third again this season. Newly-promoted Nemorino found itself outmatched and finished last with 11/28.

Division 2
Division 2 was less closely-contested. Xiphos and AllieStein dominated, finishing first and second respectively some four points ahead of everyone else. First-placed Xiphos lost two games to AllieStein, who was still improving quickly, but dominated the rest of the field, scoring 3.5/4 in its mini-matches against ChessBrainVB, rofChade, Fritz, and Nirvana. At the other end of the table, Nirvana was outclassed and finished dead last, five points from safety and without winning a single game. Former champion Fritz, which had not been updated, was also relegated for a second season in a row.

Division 1
Early favorite Komodo MCTS, who had been doing respectably in the Premier Division last season until it was disqualified for crashing, comfortably won the division with 17.5/28. Up against its strongest opponents yet, AllieStein continued to show it was improving fast enough to be able to compete, finishing second behind Komodo MCTS. Fellow promoted engine Xiphos finished third, one point behind AllieStein, after losing yet another two games to AllieStein. At the other end of the table, Italian champion Chiron finished last, three points off the pace, but the other relegation spot was closely contested. Former champion Jonny needed to hold Komodo MCTS to a draw with black in its final game to finish ahead of Fizbo, who had superior tiebreakers. It failed, and was relegated.

Premier Division
Premier division is currently ongoing.