How does an established institution incorporate deliberation by randomly selected citizens? Can they deliberate on an equal footing with interest group representatives? How do the latter envision citizen participation? This article attempts to answer these questions by analysing the deliberative mini-public 'New Generations' set up by the French Economic Social and Environmental Council (ESEC) in 2020. A socio-economic consultative assembly, the ESEC was the subject of a legislative reform adopted in January 2021, which establishes the possibility for the Council to have randomly selected citizens deliberate alongside representatives of interest groups. Relying on semi-structured interviews (n = 15), surveys at multiple points in time (n = 190), direct observation (11 days) and content analysis, we illustrate the limits of the integration of citizen deliberation within the ESEC. Articulating a longitudinal macro perspective (on the institutional and legislative transformations of the Council) with a sociological microanalysis (of the 'New Generations' experiment) allows us to underline that in the current implementation of citizens' participation in the ESEC, the institution seems to be 'flying without instruments'. Indeed, with few references to legal frameworks or scientific guidelines, the Council relies mainly on private consultants to implement deliberative practices. We thus worry that within the current political context, citizen deliberation is on its way to become an ad hoc resource, used by interest groups and institutions to defend their causes in the public sphere, but not leading to a direct implication of citizens in the decision-making process.