Which of the metadata with relevance for bibliometrics are the same and which are different when switching from Microsoft Academic Graph to OpenAlex?

With the announcement of the retirement of Microsoft Academic Graph (MAG), the non-profit organization OurResearch announced that they would provide a similar resource under the name OpenAlex. Thus, we compare the metadata with relevance to bibliometric analyses of the latest MAG snapshot with an early OpenAlex snapshot. Practically all works from MAG were transferred to OpenAlex preserving their bibliographic data publication year, volume, first and last page, DOI as well as the number of references that are important ingredients of citation analysis. More than 90% of the MAG documents have equivalent document types in OpenAlex. Of the remaining ones, especially reclassifications to the OpenAlex document types journal-article and book-chapter seem to be correct and amount to more than 7%, so that the document type specifications have improved significantly from MAG to OpenAlex. As another item of bibliometric relevant metadata, we looked at the paper-based subject classification in MAG and in OpenAlex. We found significantly more documents with a subject classification assignment in OpenAlex than in MAG. On the first and second level, the classification structure is nearly identical. We present data on the subject reclassifications on both levels in tabular and graphical form. The assessment of the consequences of the abundant subject reclassifications on field-normalized bibliometric evaluations is not in the scope of the present paper. Apart from this open question, OpenAlex seems to be overall at least as suited for bibliometric analyses as MAG for publication years before 2021 or maybe even better because of the broader coverage of document type assignments. [ABSTRACT FROM AUTHOR]