Delve exposes two API interfaces, JSON-RPC and DAP, so that frontends other than the built-in terminal client, such as IDEs and editors, can interact with Delve programmatically. The JSON-RPC API is used by the terminal client, and will always stay up to date in lockstep regardless of new features. The DAP API is a popular generic API already in use by many tools.
In order to run Delve in "API mode", simply invoke with one of the standard commands, providing the --headless flag, like so:
$ dlv debug --headless --api-version=2 --log --log-output=debugger,dap,rpc --listen=127.0.0.1:8181
This will start the debugger in a non-interactive mode, listening on the specified address, and will enable logging. The logging flags as well as the server address are optional, of course.
Optionally, you may also specify the --accept-multiclient flag if you would like to connect multiple JSON-RPC or DAP clients to the API.
You can connect to the headless debugger from Delve itself using the connect subcommand:
$ dlv connect 127.0.0.1:8181
This can be useful for remote debugging.
Delve has been architected in such a way as to allow multiple client/server implementations. All of the "business logic" as it were is abstracted away from the actual client/server implementations, allowing for easy implementation of new API interfaces.