In summary, by engineering a redox-active chiral Fe-Spiro MOF capable of sustaining SCSC confined polymerization, Cui and colleagues achieve direct atomic-scale visualization of polymer helices via SCXRD—an accomplishment previously impeded by orientational disorder. This work not only overturns the empirical assumption of wide-pore polymer growth but also establishes definitive crystallographic principles governing chirality transfer under nanoconfinement. The record-high spin polarization further provides compelling experimental validation of the intimate structure–function relationship underlying CISS. Looking ahead, the use of single-crystalline MOFs as deterministic nanoreactors offers a broadly applicable platform for studying chirality induction in diverse polymer systems, including non-conjugated backbones and alternative metal coordination environments. Given its exceptional spin-filtering performance and structural precision, this hybrid architecture holds significant promise for next-generation spintronic devices. More broadly, this work sets a benchmark for correlating complex functional phenomena with atomic-scale structure, redefining how confined polymer chemistry can be understood and exploited.