Google has launched a new Merchant API, currently in beta, in Google Merchant Center, expanding beyond the existing Content API. More details to come as the beta phase progresses.
For more information, read here: Merchant API (beta) | Google for Developers.
This news was observed by Emmanuel Flossie.
UPDATE: Archive data shared by Barry Schwartz suggests that the Merchant API webpage has been active since last year, making it unclear whether this is an official rollout or just wider availability.