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I mean the steem CLI Wallet. Does this API need any RPC IPs or similar nodes for it to work?

Ditch interacts with steemd.steemit.com through websockets by default.

However, you can write and use your custom ChainManager to interact with other nodes.

More info here https://github.com/Chainers/Ditch/blob/master/Sources/Ditch/ChainManager.cs