Abstract Many important health care interventions do not fit the classic RCT paradigm. Drug trials have struggled with issues of non-compliance and selective withdrawal. Surgical researchers have done extensive work on incorporating operator skills and experience into trial settings. Working on innovative models of care delivery related issues arise. As part of an EU funded multi-centre stepped-wedge trial, GERONTE, of nurse-led, digitally supported, health care coordination for older people with cancer and other significant co-morbidity, we have developed and tested an outline of a novel method of evaluation, drawing on realist evaluation. There are three pieces, first the central trial outcome, quality of life, for those in the trial, analysed by intention-to-treat. Second an economic evaluation, based on care pathways, and collecting costs during the control and intervention phases in 16 centres, in 3 countries. Third, a realist evaluation of implementation, with 3 phases in each site, the first of which is underway. 1) Readiness to implement GERONTE, and documenting current practice, and identifying barriers and facilitators for change with clinical staff, technical staff and administrators; 2) Experience of implementation as the intervention is brought in over the course of the study; 3) Experience in keeping GERONTE running after the initial implementation phase. Early results show great site to site variability, in practice and in resources, but common barriers are data handling and sharing. In each phase, guided by ideas from participatory rapid appraisal, we stress the rapid feedback to participants, of their response, and the synthesis of responses to support successful implementation. One aim is to prepare an implementation guide to support future deployments of GERONTE and similar projects, drawing on lessons from all 16 sites, and filling a gap in the literature. GERONTE is funded by the Horizon 2020 research and innovation programme under grant agreement No 945218. Key messages • Innovative health care delivery, such as integrated care, requires complex assessment approaches, designed for the specific innovation. • Site-to-site variability in the implementation of novel care pathways and approaches is the norm, and needs to be considered at design stage.