Traditional techniques of traceability detection and management are not equipped to handle evolution. This is a problem for the field of software architecture, where it is critical to keep synchronized an evolving conceptual architecture with its realization in an evolving code base. ArchTrace is a new tool that addresses this problem through a policy-based infrastructure for automatically updating traceability links every time an architecture or its code base evolves. ArchTrace is pluggable, allowing developers to choose a set of traceability management policies that best match their situational needs and working styles. We discuss ArchTrace, its conceptual basis, its implementation, and our evaluation of its strengths and weaknesses in a retrospective analysis of data collected from a 20 month period of development of Odyssey, a large-scale software development environment. Results are promising: with respect to the ideal set of traceability links, the policies applied resulted in 95% precision at 89% recall.