There is two kinds of Open APIs depending on their purposes:
API used to interact directly with the uns.network. All these ones are directly reachable on every nodes. (e.g this one https://forger1.sandbox.uns.network/api/uniks). Start your own relay node and get it with your own url!
API used to provide DAPPs solutions (e.g. gateways in the whitepaper) on top of the network, like Unikname Connect Authentication solution. These ones are reachable on these gateways and the level of decentralization depends on providers of these services.
Regarding Unikname Connect Authentication solution we’ve designed a scalable solution with a distributed architecture, enabling duplicate of related gateways. Most features have been developed directly on uns.network core (program running nodes). These design avoid to rely on a single and centralized server.
Released Open API are described in the API section of the documentation at docs.uns.network.