<p>This study presented a comprehensive techno-economic analysis (TEA) and life cycle assessment (LCA) of autothermal co-gasification of wood chips and waste-HDPE for sustainable hydrogen production. Unlike previous studies that primarily examined syngas composition at the gasifier outlet, this work evaluated the entire hydrogen production process, from gasification through syngas upgrading to purification, and illustrated that maximizing hydrogen content in the raw syngas would not necessarily maximize the overall hydrogen yield after downstream processing, underscoring the importance of a system-level assessment. Parametric studies on equivalence ratio (ER) and feed plastic content (FPC) revealed that while the maximum hydrogen content in the raw syngas was obtained at ER ~ 0.4, the maximum hydrogen yield along with upgrading was achieved at lower ER ~ 0.16, driven by higher methane availability for reforming. The levelized cost of hydrogen (LCoH) with 20% FPC under the optimal condition (i.e., ER ~ 0.16) achieved 45% reduction compared to cases with high ER values. Sensitivity analysis on waste plastic price identified a threshold value of $0.88/kg, below which co-gasification becomes more economically attractive than biomass-only gasification. Life Cycle Assessment (LCA) results showed carbon intensities (i.e., CO₂ emissions per kg of H₂) ranging from 3.8 to 11.1 kg-CO₂/kg-H₂ depending on FPC, increasing with higher plastic content in the feed. As hydrogen yield increased with higher FPC, these results highlighted the key trade-offs between hydrogen yield and carbon intensity, providing useful insights for process design and feedstock strategy under emerging carbon accounting frameworks, including the U.S. Inflation Reduction Act (IRA).</p>