The segmented nature of the influenza virus genome allows for the generation of novel reassortant progeny when a single cell is infected by more than one influenza virus. Since 2020, the ongoing H5N1 panzootic has led to the incursion by clade 2.3.4.4b H5 into countries with ongoing endemic circulation of diverse non-2.3.4.4b clade H5 viruses. Since 2014, Bangladesh and Cambodia have experienced endemic circulation of 2.3.2.1a and 2.3.2.1e clade H5 viruses, respectively. Clade 2.3.4.4b viruses were detected in poultry in Cambodia in 2021, and Bangladesh in 2023. Since 2023, Cambodia has reported multiple detections of novel H5 2.3.2.1e x 2.3.4.4b reassortants in humans. Similarly, an imported human case of H5 infection caused by a novel 2.3.2.1a x 2.3.4.4b genotype was reported in Australia. Whereas the novel genotype detected in Cambodia has replaced the endemic genotype, this genotype replacement has not been observed in Bangladesh. We have previously presented differences in replication kinetics between pre- and post-reassortment 2.3.2.1e viruses in a human cell model. Here, we aimed to investigate reassortment dynamics in vitro to improve our understanding of functional constraints that may help predict reassortment where viruses co-circulate. We used plaque-purified field isolates to co-infect avian cells, simulating natural reassortment events. Following co-infection, we plaque-purified and sequenced viruses to quantify gene exchange. We found high levels of reassortment between 2.3.2.1 and 2.3.4.4b viruses with few constraints on gene exchange. These findings have significant impact on pandemic risk assessment, highlighting the importance of surveillance to identify novel genotypes in different ecological niches.