Wikibase Solutions has been leading the initiative
On the Semantic MediaWiki conference in 2020 Ad Strack van Schijndel did a presentation on the subject. That can be regarded as the start of the initiative.
Since then Wikibase Solutions has been promoting the Open CSP and developing extensions.
Wikibase Solutions is maintainer of the software
Open CSP is open source software that anybody can contribute to. The role of Wikibase Solutions is the maintainer of the software. This means that they review proposed changes, communicate about it and merge them in the software. The maintainer is responsible for the quality of the software.
Wikibase Solutions provides services for your Content Services Platform
Wikibase Solutions provides services that enable you to realize the full potential of a Content Services Platform in your organization.