Multi-sector coupling holds the potential for increasing flexibility. But what are the beneficial and detrimental impacts of system flexibilisation, and how can we assess and anticipate them? The objective of this IEA Bioenergy, IEA ETSAP and IEA Hydrogen collaboration is to exchange modelling experiences and perspectives on the multi-faceted aspects of flexibility. A bioenergy supply chain can be an intricate and networked affair: Flexibility can often be found throughout the chain, in feedstock sourcing, pre-treatment, storage, distribution, and conversion into heat, power, and fuels. While hydrogen supply and utilisation from feedstock-independent renewables might be a less complex endeavour, respective impact assessment is not straightforward either. For example, energy storage at different time scales, inter-sectoral synergies and tradeoffs, and contributions to energy security must be accounted for. Also, system complexification through integration, sector-, and multi-sector coupling boosts systemic risks, encompassing safety concerns, security vulnerabilities, and the potential for cascading failures. Adjunct to the ETSAP workshop and ExCo meeting in Torino (IT), a half-day workshop will set the scene for the discussion and the joint planning of a webinar with the aim of formulating a modelling agenda for flexibilisation impact assessment. Your participation and expertise are invaluable to shaping this discourse. We eagerly anticipate your presence for the interdisciplinary and inclusive exchange.