  The road map to the FCC Feasibility Study Report, for submission to the next
Update of the European Strategy for Particle Physics, will require detailed
simulation and advanced reconstruction algorithms to explore and maximise the
physics reach of proposed detector solutions. The optimisation process will
require maximal flexibility in changing detector geometries, materials and
sensitive areas, and efficient tools to quantify the overall performance. To
synergise such developments the CEPC, CLIC, FCC, ILC and SCT communities have
engaged in the commissioning of a `Turnkey Software Stack' (Key4hep), which
would provide all the necessary ingredients, from simulation to analysis, for
future experiments. This approach is based on the positive experience of the
linear collider projects ILC and CLIC, which have developed and used a common
software stack (iLCSoft) over the last decade. Key4hep aims to cover most, if
not all, future linear and circular machines colliding leptons (electrons,
muons), and hadrons. The common software ecosystem will facilitate writing
specific components for experiments ensuring coherency and maximising the
re-use of established solutions. Project-specific software frameworks will
require adaptation to fully profit from the common software base. In this essay
we present the status and plans for re-framing the FCC software framework,
FCCSW, around Key4hep and discuss the challenges associated with the
transition.
