How Effective Is Mamba-Augmented Transformer for Stock Market Price Forecasting?

Stock price forecasting remains challenging due to the non-linear, noisy, and non-stationary nature of financial time series. Although LSTMs and Transformer-based models have improved sequential modeling, their ability to scale efficiently to long financial sequences remains limited. Recently, selective state space models such as Mamba have emerged as efficient alternatives to self-attention, offering attention-like performance with linear computational complexity. In this study, we systematically evaluate multiple Mamba-augmented Transformer architectures for stock market price forecasting. We further propose CrossMamba, a novel architecture that models cross-sequence interactions between encoder and decoder representations using a causal Mamba block. Experiments on multiple S&P 500 and Yahoo Finance stocks show that CrossMamba achieves superior short-horizon performance with 5-day input windows (R2 up to 0.963), while Hybrid Bi-Mamba performs best for longer horizons, achieving the lowest MAE of 0.67 for 10-day forecasts. Compared with advanced Mamba-based and Transformer baselines, the proposed models achieve competitive accuracy while maintaining substantially improved computational efficiency. These results highlight the effectiveness of Mamba-augmented Transformers as scalable architectures for financial time series forecasting.