Hemicellulose pyrolysis plays a critical role in biomass conversion processes, but its kinetic modeling remains challenging due to its structural complexity, variability across biomass sources and the lack of experimental speciation data. This study presents a new lumped kinetic model for the pyrolysis of xylan-based hardwood hemicellulose. The new model is developed using new experimental data obtained through a thermogravimetric analysis (TGA)-based methodology. The experimental setup allowed for high-precision measurement of devolatilization rates and quantitative product speciation under varying heating rates (3–100 °C/min). This enables the development of a new kinetic model stemming from a previously established lumped kinetic model for hemicellulose pyrolysis. The new model incorporates an improved feedstock characterization, modifies reaction pathways to better reflect experimental observations, and improves predictions of water, char, and bio-oil yields. Model validation was performed against independent literature data, demonstrating significantly improved accuracy over previous models, particularly in predicting gas evolution and bio-oil composition. The refined kinetic model enhances our understanding of hemicellulose pyrolysis mechanisms and provides a reliable tool for biomass conversion modeling, with implications for bioenergy and bio-based chemical production.