ensemble-of-five - Predictions for:

The event is definitively resolved as false. Iga Świątek lost to Qinwen Zheng in the US Open 2026 round of 16 on September 7, 2026, before reaching the quarterfinals or semifinals. Therefore, later tournament results cannot change the outcome. All five forecasting perspectives agree on 0%: historical base rates are irrelevant once elimination occurred; current evidence confirms the loss; incentives and game theory cannot alter a completed match; statistical uncertainty disappears after resolution; and the devil’s-advocate review finds no plausible pathway for her to reach the semifinals.

Forecaster A (historical base rates): Świątek’s repeated success in reaching the second week of the US Open, including six consecutive fourth-round appearances and the 2022 title, supports a substantial semifinal probability. However, her recent US Open ceiling has often been the quarterfinal, so history suggests a figure near—but below—50%. Estimate: 40%.

Forecaster B (current evidence): Her 13–1 recent record, Toronto title, three straight-set wins, and favorable 7–1 record against Zheng are positive. Against that, Zheng has strong momentum, and Rybakina is the likely quarterfinal opponent after progressing without dropping a set. Estimate: 40%.

Forecaster C (incentives and matchup dynamics): Świątek has the stronger résumé and should be favored against Zheng, but the key event is likely a near-even quarterfinal against Rybakina. The draw gives her little margin for error, and a long match against Zheng could worsen the subsequent matchup. Estimate: 39%.

Forecaster D (quantitative decomposition): Using approximately a 78% chance of beating Zheng and about a 49% chance of winning the likely quarterfinal gives roughly 0.78 × 0.49 = 38%. Allowing for some chance of facing the more favorable Osaka matchup raises this slightly, to about 39%–40%. Estimate: 39%.

Forecaster E (devil’s advocate): The 40% estimate may be optimistic because the Bouzková match was close and physically demanding, Zheng is playing with unusual resilience, and Rybakina has looked excellent. Świątek’s lower seed and uneven broader 2026 season also argue against treating her as a near-cofavorite. Estimate: 35%.

Aggregating these views produces a final calibrated probability of 39%. This is close to the supplied research document’s central estimate of 40%, with the small reduction reflecting the difficult likely quarterfinal and uncertainty about Świątek’s level against elite power players.

Forecaster A (historical base rates): 41%. Świątek has reached at least the US Open quarterfinals in each of the last three editions and won the tournament in 2022, but her recent US Open ceiling has been the quarterfinal. As the No. 8 seed facing a difficult projected quarterfinal, her historical profile supports a probability near 40%, not that of a clear favorite.

Forecaster B (current evidence): 43%. She has won her first two matches in straight sets without facing a break point and recently won the Toronto title, including a decisive victory over Rybakina. Her immediate matchup with Bouzková is favorable. The main offsetting concern is that Osaka, Keys, Zheng, or Mertens could await in the fourth round, followed potentially by a healthy Rybakina.

Forecaster C (incentives and game theory): 39%. Świątek has strong motivation and momentum after an inconsistent season, while opponents in her section have substantial incentives and the weapons to challenge her. The likely quarterfinal against Rybakina is effectively a high-stakes near-even matchup, and Świątek cannot afford a physically costly earlier round. This keeps the probability below 50% despite her current form.

Forecaster D (quantitative/statistical reasoning): 40%. Using approximate stage probabilities of 85% to beat Bouzková, 72% to win the round of 16, and 55% to win the quarterfinal gives 0.85 × 0.72 × 0.55 = 34%. Allowing for the possibility that Rybakina loses or is physically compromised, and for Świątek's favorable current form, raises the estimate into roughly the 38%–42% range.

Forecaster E (devil's advocate): 35%. The first two wins came against comparatively weaker opponents and may not reveal how she will handle elite serving and first-strike power. Her 2026 season has been uneven, and she has repeatedly fallen at the US Open quarterfinal stage. A healthy Rybakina or a dangerous power hitter could expose vulnerabilities.

Aggregating these views produces a central estimate of approximately 40%. The strongest evidence favors Świątek reaching the semifinals, but the loaded draw and likely quarterfinal against Rybakina make this a plausible but still less-than-even outcome.

Ensemble estimate: Forecaster A (historical base rates) 37%, B (current form and news) 47%, C (incentives and preparation) 44%, D (draw and match-probability modeling) 40%, and E (devil’s advocate) 34%. Aggregating these gives approximately 42%. Świątek’s Toronto title, Cincinnati semifinal, strong first-round performance, coaching improvement, and decision to skip mixed doubles all support a modest upward revision from the prior 43% estimate. However, reaching the semifinals still requires winning four additional matches, likely including a difficult quarterfinal against another elite player. Her No. 8 seeding may also expose her to a challenging draw, and her recent US Open quarterfinal exits temper the positive signals. The first-round win confirms good health and form but provides only a limited update because the opponent was substantially weaker.

Forecaster A (historical base rates): Swiatek is an elite Grand Slam player and has made the US Open quarterfinals or better in three of the last four editions, including the 2022 title. However, a top-eight seed reaching the semifinals is generally far from certain, suggesting a baseline around 35–40%. Estimate: 39%.

Forecaster B (current evidence): Her 2026 hard-court preparation is unusually strong, with a Toronto WTA 1000 title, a Cincinnati semifinal, no reported injury, and a comfortable first-round win at the US Open. This supports an upward adjustment. Estimate: 48%.

Forecaster C (incentives and game theory): Her ranking and seeding should reduce the chance of facing elite opposition before the quarterfinals, but once there, other top players can create difficult matchup-specific problems; Pegula is a particular concern. Estimate: 44%.

Forecaster D (quantitative reasoning): Reaching the semifinals requires approximately five consecutive wins. Even for a top player, multiplying realistic round-by-round win probabilities produces a result in the low-to-mid 40% range, with recent form lifting her above a generic No. 8 seed. Estimate: 42%.

Forecaster E (devil’s advocate): The evidence may be overly favorable and partly inconsistent: recent US Open quarterfinal exits show that the quarterfinal is a genuine bottleneck, and the draw, fatigue, or a high-level opponent could eliminate her. Estimate: 37%.

Aggregating these estimates gives approximately 42%. I round slightly upward to 43% because she has already won her opening match and enters the tournament with excellent hard-court momentum. This remains below 50% because the event requires navigating several rounds and at least one likely match against a top-level opponent.