Programmatic Integration

Hermes ships three protocols for driving the agent from external programs — IDE plugins, custom UIs, CI pipelines, embedded sub-agents. Pick the one that matches your transport and consumer.

All three drive the same AIAgent core. They differ only in wire format and which set of features they expose.

ACP (Agent Client Protocol)

hermes acp starts a stdio JSON-RPC server speaking ACP. Used in production by VS Code (Zed Industries' ACP extension), Zed, and any JetBrains IDE with an ACP plugin.

Capabilities exposed: session creation, prompt submission, streaming agent message chunks, tool-call events, permission requests, session fork, cancel, and authentication. Tool output is rendered into ACP Diff/ToolCall content blocks the IDE understands.

Full lifecycle, event bridge, and approval flow: ACP Internals.

hermes acp                  # serve ACP on stdio
hermes acp --bootstrap      # print install snippet for an ACP-capable IDE

TUI Gateway JSON-RPC

tui_gateway/server.py is the protocol the Ink TUI (hermes --tui) and the embedded dashboard PTY bridge talk to. Any external host can speak the same protocol over stdio (or WebSocket via tui_gateway/ws.py).

Method catalog (selected)

prompt.submit           prompt.background       session.steer
session.create          session.list            session.active_list
session.activate        session.close           session.interrupt
session.history         session.compress        session.branch
session.title           session.usage           session.status
clarify.respond         sudo.respond            secret.respond
approval.respond        config.set / config.get commands.catalog
command.resolve         command.dispatch        cli.exec
reload.mcp              reload.env              process.stop
delegation.status       subagent.interrupt      spawn_tree.save / list / load
terminal.resize         clipboard.paste         image.attach

session.active_list, session.activate, and session.close are the process-local live-session controls used by the TUI session switcher. Use session.list / /resume for saved transcript discovery; use the active-session methods only for sessions that are currently open in the TUI gateway process.

Events streamed back

message.delta, message.complete, tool.start, tool.progress, tool.complete, approval.request, clarify.request, sudo.request, secret.request, gateway.ready, plus session lifecycle and error events.

Pi-style RPC mapping

Every command in the Pi-mono RPC spec (issue #360) has a TUI-gateway equivalent:

OpenAI-Compatible API Server

gateway/platforms/api_server.py exposes hermes over HTTP for any client that already speaks the OpenAI format. Useful when you want a web frontend, a curl-driven CI runner, or a non-Python consumer.

Endpoints:

POST /v1/chat/completions        OpenAI Chat Completions (streaming via SSE)
POST /v1/responses               OpenAI Responses API (stateful)
POST /v1/runs                    Start a run, returns run_id (202)
GET  /v1/runs/{id}               Run status
GET  /v1/runs/{id}/events        SSE stream of lifecycle events
POST /v1/runs/{id}/approval      Resolve a pending approval
POST /v1/runs/{id}/stop          Interrupt the run
GET  /v1/capabilities            Machine-readable feature flags
GET  /v1/models                  Lists hermes-agent
GET  /health, /health/detailed

Setup, headers (X-Hermes-Session-Id, X-Hermes-Session-Key), and frontend wiring: API Server.

Which one should I use?

• You're writing an IDE plugin and the IDE already speaks ACP → ACP. Zero protocol work on the IDE side.
• You're writing a custom desktop / web / TUI host and want every Hermes feature (slash commands, approvals, clarify, multi-agent, session branching) → TUI gateway JSON-RPC.
• You want any OpenAI-compatible frontend, a language-agnostic HTTP client, or curl-driven automation → API server.
• You want a Python in-process embed without a subprocess → import run_agent.AIAgent directly. See Agent Loop.

Model hot-swapping

Mid-session model switching works on every surface — it's the /model slash command under the hood.

• CLI / TUI: /model claude-sonnet-4 or /model openrouter:anthropic/claude-sonnet-4.6
• TUI gateway RPC: command.dispatch with {"command": "/model claude-sonnet-4"}
• ACP: the IDE sends the slash command as a prompt; the agent dispatches it
• API server: include a model field in the request body or set X-Hermes-Model

Provider-aware resolution (the same model name picks the right format for whatever provider you're on) is built in. See hermes_cli/model_switch.py.

A note on --mode rpc

Hermes does not have a --mode rpc flag. The three protocols above already cover the use cases — ACP for IDE-protocol clients, the TUI gateway for stdio JSON-RPC hosts, and the API server for HTTP. If you find a real gap that none of them fill, open an issue with the concrete consumer you're building.