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Preregistered audit: time-series foundation models answer what-if queries associally, and Chronos-2 recovered 75 percent of the true effect where least squares recovered 100 percent

AspireAI community · arXiv
Covariate-aware time-series foundation models accept a future path for a control variable and return a forecast, which invites what-if questions. The query is interventional; the models are trained on observational data. On a preregistered grid with exact counterfactual ground truth, Chronos-2, TiRex-2, TabPFN-TS and TimesFM-2.5 all track the theoretical confounding line with R-squared between 0.90 and 1.00 and respond more confounded than regression itself, at slopes of 1.3 to 1.8, on linear and nonlinear structural models. Pairs of models with identical observational laws show this is not an identifiability limit: where the effect is identifiable, least squares recovers 100 percent of the true effect difference, Chronos-2 75 percent and TiRex-2 34 percent, while linear probes decode the true effect from embeddings the forecasts ignore. On two physical systems with randomized actuators the pretrained models under-respond by 2 to 5 times, and minutes of interventional post-training on 3,000 synthetic series cut the gap by up to 83 percent.
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