6arXiv cs.CL (Computation and Language)·
Hindcast: A benchmark framework that closes data-leakage loopholes in LLM forecasting evaluation
A new arXiv preprint introduces Hindcast, an evaluation framework for LLM forecasters that addresses two systematic data-leakage channels in standard backtesting: post-event retrieval and training-data contamination from newer models. The system replays resolved Polymarket prediction markets against a frozen Reddit snapshot, grading models only on information available before a chosen cutoff date and comparing against contemporaneous market prices as a human-forecast baseline. Key finding: retrieval helps forecasting only when pre-event Reddit discussion existed; where only speculation was available, retrieval hurts performance. The framework is designed to remain valid as new models and markets emerge without going stale.
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HypoArena benchmark evaluates LLMs on open-ended hypothesis discovery before conclusions are known
Researchers introduce Prospective Hypothesis Discovery (PHD), a new capability framing that tests whether LLMs can autonomously generate grounded, testable hypotheses from inconclusive evidence rather than answering pre-specified questions. The benchmark HypoArena includes 988 cases across six scientific and analytical domains, constructed via a novel Retrospective Context Regression pipeline that strips conclusions from expert documents. Evaluation of 15 frontier LLMs using a Bradley-Terry-Davidson arena framework reveals clear capability stratification and model-dependent effects of structured analytical prompting, with some models regressing under structured guidance. The work positions hypothesis formulation as a distinct, underexplored evaluation target for LLMs.
Bayesian audit framework for public AI evaluation archives challenges frontier model claims
A new arXiv preprint proposes a Bayesian inference and decision-audit framework for interpreting public AI evaluation archives (LiveBench, Open LLM Leaderboard v2, LMArena, GAIA, tau-bench) as longitudinal time series rather than terminal leaderboards. The paper demonstrates that a single terminal snapshot is compatible with multiple distinct performance histories, yielding ambiguous timing estimates for reaching capability ceilings. A candidate selection-aware frontier model is shown to fail synthetic recovery, objective-archive prediction, preference transfer, and uncertainty calibration, with fixed audit gates rejecting its stronger claims. The work proposes an archive-and-adjudication protocol to reconstruct evaluation histories and falsify unsupported frontier capability claims.
LLM Agent Framework for Last-Mile Time Series Forecasting Revision
This paper introduces a 'last-mile forecasting' framework where an LLM agent sits atop a statistical forecasting backbone to incorporate weakly structured business context—holidays, campaigns, expert feedback, external events—into decision-ready forecasts. The system uses tool-invocation for contextual retrieval, converts reasoning into explicit revision actions under safety constraints, and supports long-horizon forecasting via map-reduce decomposition with a memory bank for post-hoc reflection. The authors validate the approach through real-world case studies, positioning it as a bridge between statistical prediction and operationally usable forecasts.
StakeBench: A Market-Commitment-Grounded Benchmark for Financial Language Understanding
StakeBench is a new evaluation framework linking 560,876 comments from 2,261 resolved prediction markets (Polymarket and Manifold) to verified trading positions, actions, and market-odds records, replacing human annotation with observable market behavior as supervision. Four diagnostic tasks test commitment detection, side identification, action anticipation, and collective odds projection, evaluated across 15 LLMs. Results reveal structural failures: models partially recover position-side signals (Directed Accuracy 0.506–0.599) but collapse on action anticipation and fail to beat naive baselines on odds projection. Notably, model scale shows no correlation with performance, and finance-domain fine-tuning does not improve revealed-side identification.
Forecasting Downstream LLM Performance With Token-Level Proxy Metrics
Researchers propose proxy metrics constructed from token-level statistics (entropy, top-k accuracy, expert token rank) drawn from a candidate model's next-token distribution over expert-written solutions, as a cheaper and more reliable alternative to cross-entropy loss or direct downstream evaluation. Across three settings—cross-family model selection, pretraining data selection, and training-time forecasting—the proxies consistently outperform baselines, achieving mean Spearman Rho of 0.81 vs. 0.36 for cross-entropy loss on model ranking, and reducing compute for data selection by roughly 10,000×. The method enables downstream performance extrapolation across an 18× compute horizon with roughly half the error of existing alternatives, suggesting expert trajectories are broadly useful signals throughout the model development lifecycle.
Benchmark of deep learning architectures for multi-horizon behavioural forecasting in mobile health
A new arXiv preprint benchmarks six deep learning architectures, two zero-shot foundation models, and statistical baselines on multi-horizon behavioural forecasting from wearable and smartphone data across 800+ participants. Key findings include: no single architecture dominates (PatchTST leads among trained models), TimesFM matches or exceeds trained models zero-shot especially in low-data regimes, and participant-level fine-tuning reduces per-feature RMSE by 16–60%. The study is the first to jointly evaluate modern deep learning, foundation models, and personalisation for this domain.
Zero-shot LLMs fail to beat baselines on stock prediction; explainability signals retain practical value
A new arXiv preprint evaluates zero-shot NLP pipelines for predicting short-term stock movements from financial news, finding that across multiple models and prediction horizons, zero-shot approaches consistently fail to outperform simple baselines, with especially weak performance on negative price movements. The authors introduce a multi-layered explainability framework linking predictions to token-, article-, and aggregate-level evidence, finding that explainability signals can reliably distinguish trustworthy from unreliable predictions even when accuracy is low. The work argues for a shift toward decision-support systems emphasizing transparency and uncertainty awareness rather than raw predictive accuracy.
Stance Detection in Prediction Market Commentary via Counterfactual Augmentation and Market Context
This paper introduces the first stance detection system applied to prediction market commentary (Polymarket), addressing extreme class imbalance (8.7% anti-market comments) through LLM-driven counterfactual augmentation using the Anthropic API. RoBERTa-base is fine-tuned across a 4×3 ablation covering input configurations and augmentation doses. Key findings: market context is the dominant factor (raising 3-class Anti recall from 0.10 to 0.45), 50% synthetic augmentation is optimal, and full augmentation (100%) consistently degrades performance. Attention-based interpretability supports all three findings mechanistically.