Yes, quite a bit is retrievable, and it's all through the Unity Catalog REST API. The catch is that it's documented inline on the Register agents (agent services) page rather than as a standalone entry in the API reference, which is why you couldn't find it.
What's stored on the record. An Agent Service holds its resource name (e.g. main.default.support_agent), the agent_service_type (currently AGENT_SERVICE_TYPE_EXTERNAL), a comment, the source UC connection under config.source_connection.name (which holds the external host and credentials), config.base_path, config.system_prompt, and created_by. There's no richer remote-agent model documented, so nothing on capabilities, tools, model info, version or health. Permissions live separately, with assignable privileges of EXECUTE, READ METADATA, MANAGE and ALL PRIVILEGES (source).
How to retrieve it (GET operations, all on that same page):
# One service
databricks api get "/api/2.1/unity-catalog/agent-services/main.default.support_agent"
# List within a schema
databricks api get "/api/2.1/unity-catalog/agent-services?parent=schemas/main.default"
# List across the metastore
databricks api get "/api/2.1/unity-catalog/agent-services"
# Permissions
databricks api get "/api/2.1/unity-catalog/permissions/AGENT_SERVICE/main.default.support_agent"
Is the API available? Yes for registration and management, but the feature is still Beta, so an account admin has to switch on the Unity Gateway beta features from the account console Previews page first.
Two things to expect in this release. Runtime invocation isn't there yet:
"Runtime invocation is not available. Agents cannot be called through a registered agent service."
And full_name and owner come back null on GET responses in this release. There's no SQL DDL either, so management is UI or REST only.
Full reference: https://docs.databricks.com/aws/en/ai-gateway/agent-services