From Springer Nature:
Springer Nature becomes the largest academic publisher to open up reference lists to advance data discovery and reuse, effective as of today. Working closely with Crossref, Springer Nature will make the metadata for reference lists available across all academic books and owned journals (and as an option for society partners.)
The references are available through the Crossref Metadata APIs and Metadata Search including the ‘link references’ tool for matching references to DOIs.
Steven Inchcoombe, Chief Publishing Officer adds: “From open access, to open data, and now open citations. We will be the largest major publisher to make all our citation metadata freely available through Crossref.