Openings › Monthly reports › Sep 2026
Opening Report: What Moved on Lichess
Was the Italian Game: Giuoco Piano played more at 1500–1799 (Lichess rating) in September 2026? Its share moved from 1.28% to 1.43% (observed; no cause claimed).
1 change outside the margin, at 1 Lichess rating level.
In Lichess games of September 2026 compared with August 2026, the largest change outside the margin was the Italian Game: Giuoco Piano at 1500–1799 (Lichess rating): its share moved from 1.28% to 1.43% (1,769 and 1,879 games). Observed results, not causation.
- Games of: September 2026, compared with the games of August 2026 (two separate monthly samples)
- Games in the samples: 480,661 (August 2026) and 456,087 (September 2026)
- Published: 14 Oct 2026
Changes outside the margin
| Opening | Lichess rating level | Measure | August 2026 | September 2026 | Change | Standard errors |
|---|---|---|---|---|---|---|
| Italian Game: Giuoco Piano | 1500–1799 | Share of games | 1.28% (1,769 games) | 1.43% (1,879 games) | +0.15 points (+12%) | 3.3 |
- Was the Italian Game: Giuoco Piano played more at 1500–1799 (Lichess rating) in September 2026? Its share moved from 1.28% to 1.43% (observed; no cause claimed).
232 pairs of opening and Lichess rating level had at least 300 games in both months and were compared (60 openings, 5 levels). The others are left out, never counted as a change.
How this report is made
- It compares the games of the report month against the games of the month before: two separate monthly samples. It never compares two overlapping 12-month windows.
- Games: rated Lichess games, both players at most 200 rating points apart, excluded terminations removed, bullet, blitz, rapid and classical together; level = average Lichess rating of both players.
- Share = games that reached the position at the level / all used games at the level. Score = the choosing side's wins + half the draws / games that reached the position at the level.
- Each pair needs at least 300 games at that level in both months.
- Standard error of a share: sqrt(p * (1 - p) / N); of a score: sqrt((E[x^2] - s^2) / n), x = 1, 1/2 or 0; of a change: sqrt(SE_previous^2 + SE_current^2).
- A change is listed only at 3 standard errors or more and at least 10% relative change (share) or 0.5 points (score). The rules were fixed before the numbers were read; a quiet month is a valid result.
- Caution: each monthly sample is made of blocks of consecutive games (the slices of the monthly file), not a random draw: the standard errors are optimistic, so real uncertainty is larger than shown.
- These are observed changes in a sample of Lichess games. They say nothing about why a change happened.
Download this report's frozen numbers: Sep 2026 report (JSON), CC0, like the Lichess data it comes from. Feed: all monthly reports (Atom).