LLMs for Time Series: an Application for Single Stocks and Statistical Arbitrage
LLMs for Time Series: an Application for Single Stocks and Statistical Arbitrage
This paper investigates whether Large Language Models (LLMs) adapted for time series forecasting can predict financial market returns, which are often considered nearly random. The authors use the Chronos model, a pretrained time-series foundation model with 11 million parameters, and apply it to daily residual returns of the largest U.S. stocks from 1978 to 2016. Residual returns are extracted using three methods: IPCA, PCA, and Fama-French factors, following the dataset of Guijarro-Ordonnez et al. (2021). The study employs both zero-shot (no fine-tuning) and fine-tuned versions of Chronos, where fine-tuning involves daily retraining on the available data. Portfolio weights are determined by ranking predicted returns and taking long/short positions proportional to rank distance from the median, with volatility scaling to manage risk. The main finding is that Chronos, even without any financial training data, can generate significant alpha, with gross Sharpe ratios exceeding 1.3 across all residual datasets. Fine-tuning further improves performance, achieving Sharpe ratios above 2.0. These results surpass traditional benchmarks such as Short-Term Reversal (STR), autoARIMA, and a smaller CNN-Transformer model. The paper concludes that LLMs can identify inefficiencies in financial time series that are nearly indistinguishable from noise, offering a promising tool for quantitative trading strategies. The authors also note that fine-tuning requires careful control to avoid overfitting, and that the pretrained model's zero-shot performance is particularly convincing as it minimizes overfitting concerns.
Highlights
- 1First application of a large language model (LLM) with over 11 million parameters to financial time series forecasting for single stocks.
- 2Demonstrates that zero-shot pretrained Chronos model can generate significant alpha from residual returns, challenging the belief that financial returns are unpredictable.
- 3Fine-tuning Chronos on financial data further improves performance, achieving gross Sharpe ratios above 2.0.
- 4Outperforms traditional benchmarks including Short-Term Reversal (STR), ARIMA, and a small CNN-Transformer model.
Methods
- MZero-shot evaluation using the pretrained Chronos-T5-tiny model (11M parameters) on daily residual returns from IPCA, PCA, and Fama-French factor models.
- MFine-tuning Chronos with daily retraining (τ=5, 15, 40) on the same residual returns, using a rolling window of 100 days.
- MPortfolio construction based on ranking of predicted returns, with weights proportional to rank distance from median and volatility scaling.
- MComparison against benchmarks: Short-Term Reversal (STR), autoARIMA, and a CNN-Transformer model from prior literature.
Results
- RZero-shot Chronos with α=0.3 achieves gross Sharpe ratios of 1.64 (IPCA), 1.59 (PCA), and 1.30 (FF) on residual returns.
- RFine-tuned Chronos (τ=15) yields higher Sharpe ratios: 2.15 (IPCA), 2.10 (PCA), and 1.85 (FF).
- ROutperforms STR (Sharpe ~0.8-1.0), autoARIMA (Sharpe ~0.5-0.7), and the CNN-Transformer (Sharpe ~1.0-1.2) across all datasets.
- RPerformance is robust across different residual extraction methods and volatility scaling improves Sharpe by ~0.1-0.2.
- RWeightWatcher analysis confirms no overfitting in fine-tuned models (power-law exponents between 2 and 6).
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