In short
The Data Manager API is Google’s unified interface for bringing first-party conversions and audiences into Google Ads and related products, consolidating several older upload paths into one. It applies privacy-enhancing technology by default and is the integration surface Google uses for its named data partners, which makes it the modern replacement for the patchwork of separate offline-import and audience-upload endpoints advertisers used to stitch together. For an advertiser, the practical significance is consistency: one API to send conversions and audiences, with hashing and consent handling built into the contract rather than bolted on per destination. For a partner, integration with the Data Manager API is a signal of standing in Google’s ecosystem, because the API is how Google expects first-party data to arrive. Datahash is integrated with the Data Manager API, so conversions and audiences move into Google through the interface Google itself designed for the purpose rather than through legacy uploads.
Where Datahash fits
Datahash is one of the API-integrated partners Google lists for the Data Manager API, and implements it end to end across Ads, GA4, and downstream products.
What does the Data Manager API replace?
Where an advertiser once maintained separate offline-conversion imports and audience uploads, the Data Manager API carries both through one interface with privacy-enhancing technology applied by default. Datahash sends conversions and audiences into Google over this API rather than legacy paths.
Reference: Google for Developers, Data Manager API