After more than 15 years in service, although most of them working pretty unreliably, OSM History Viewer has been finally shut down on 2025-03-09.
A rewrite of its functionality has been integrated into FacilMap. To visualize
a changeset, type changeset <id> (for example changeset 6798641) into its search
field. To blame a relation, type blame relation <id>. You can also blame ways now by typing
blame way <id>. Find out more
in the OSM Wiki.
You can still access the source code and documentation of the old version.