OpenAI-Compatible API Server for Hermes Agent

Motivation

Every major chat frontend (Open WebUI 126k★, LobeChat 73k★, LibreChat 34k★, AnythingLLM 56k★, NextChat 87k★, ChatBox 39k★, Jan 26k★, HF Chat-UI 8k★, big-AGI 7k★) connects to backends via the OpenAI-compatible REST API with SSE streaming. By exposing this endpoint, hermes-agent becomes instantly usable as a backend for all of them — no custom adapters needed.

What It Enables

┌──────────────────┐
│  Open WebUI      │──┐
│  LobeChat        │  │    POST /v1/chat/completions
│  LibreChat       │  ├──► Authorization: Bearer <key>     ┌─────────────────┐
│  AnythingLLM     │  │    {"messages": [...]}             │  hermes-agent   │
│  NextChat        │  │                                    │  gateway        │
│  Any OAI client  │──┘    ◄── SSE streaming response      │  (API server)   │
└──────────────────┘                                        └─────────────────┘

A user would:

1. Set API_SERVER_ENABLED=true in ~/.hermes/.env
2. Run hermes gateway (API server starts alongside Telegram/Discord/etc.)
3. Point Open WebUI (or any frontend) at http://localhost:8642/v1
4. Chat with hermes-agent through any OpenAI-compatible UI

Endpoints

Architecture

Option A: Gateway Platform Adapter (recommended)

Create gateway/platforms/api_server.py as a new platform adapter that extends BasePlatformAdapter. This is the cleanest approach because:

• Reuses all gateway infrastructure (session management, auth, context building)
• Runs in the same async loop as other adapters
• Gets message handling, interrupt support, and session persistence for free
• Follows the established pattern (like Telegram, Discord, etc.)
• Uses aiohttp.web (already a dependency) for the HTTP server

The adapter would start an aiohttp.web.Application server in connect() and route incoming HTTP requests through the standard handle_message() pipeline.

Option B: Standalone Component

A separate HTTP server class in gateway/api_server.py that creates its own AIAgent instances directly. Simpler but duplicates session/auth logic.

Recommendation: Option A — fits the existing architecture, less code to maintain, gets all gateway features for free.

Request/Response Format

Chat Completions (non-streaming)

POST /v1/chat/completions
Authorization: Bearer hermes-api-key-here
Content-Type: application/json

{
  "model": "hermes-agent",
  "messages": [
    {"role": "system", "content": "You are a helpful assistant."},
    {"role": "user", "content": "What files are in the current directory?"}
  ],
  "stream": false,
  "temperature": 0.7
}

Response:

{
  "id": "chatcmpl-abc123",
  "object": "chat.completion",
  "created": 1710000000,
  "model": "hermes-agent",
  "choices": [{
    "index": 0,
    "message": {
      "role": "assistant",
      "content": "Here are the files in the current directory:\n..."
    },
    "finish_reason": "stop"
  }],
  "usage": {
    "prompt_tokens": 50,
    "completion_tokens": 200,
    "total_tokens": 250
  }
}

Chat Completions (streaming)

Same request with "stream": true. Response is SSE:

data: {"id":"chatcmpl-abc123","object":"chat.completion.chunk","choices":[{"index":0,"delta":{"role":"assistant"},"finish_reason":null}]}

data: {"id":"chatcmpl-abc123","object":"chat.completion.chunk","choices":[{"index":0,"delta":{"content":"Here "},"finish_reason":null}]}

data: {"id":"chatcmpl-abc123","object":"chat.completion.chunk","choices":[{"index":0,"delta":{"content":"are "},"finish_reason":null}]}

data: {"id":"chatcmpl-abc123","object":"chat.completion.chunk","choices":[{"index":0,"delta":{},"finish_reason":"stop"}]}

data: [DONE]

Models List

GET /v1/models
Authorization: Bearer hermes-api-key-here

Response:

{
  "object": "list",
  "data": [{
    "id": "hermes-agent",
    "object": "model",
    "created": 1710000000,
    "owned_by": "hermes-agent"
  }]
}

Key Design Decisions

1. Session Management

The OpenAI API is stateless — each request includes the full conversation. But hermes-agent sessions have persistent state (memory, skills, tool context).

Approach: Hybrid

• Default: Stateless. Each request is independent. The messages array IS the conversation. No session persistence between requests.
• Opt-in persistent sessions via X-Session-ID header. When provided, the server maintains session state across requests (conversation history, memory context, tool state). This enables richer agent behavior.
• The session ID also enables interrupt support — a subsequent request with the same session ID while one is running triggers an interrupt.

2. Streaming

The agent's run_conversation() is synchronous and returns the full response. For real SSE streaming, we need to emit chunks as they're generated.

Phase 1 (MVP): Run agent in a thread, return the complete response as a single SSE chunk + [DONE]. This works with all frontends — they just see a fast single-chunk response. Not true streaming but functional.

Phase 2: Add a response callback to AIAgent that emits text chunks as the LLM generates them. The API server captures these via a queue and streams them as SSE events. This gives real token-by-token streaming.

Phase 3: Stream tool execution progress too — emit tool call/result events as the agent works, giving frontends visibility into what the agent is doing.

3. Tool Transparency

Two modes:

• Opaque (default): Frontends see only the final response. Tool calls happen server-side and are invisible. Best for general-purpose UIs.
• Transparent (opt-in via header): Tool calls are emitted as OpenAI-format tool_call/tool_result messages in the stream. Useful for agent-aware frontends.

4. Authentication

• Bearer token via Authorization: Bearer <key> header
• Token configured via API_SERVER_KEY env var
• Optional: allow unauthenticated local-only access (127.0.0.1 bind)
• Follows the same pattern as other platform adapters

5. Model Mapping

Frontends send "model": "hermes-agent" (or whatever). The actual LLM model used is configured server-side in config.yaml. The API server maps any requested model name to the configured hermes-agent model.

Optionally, allow model passthrough: if the frontend sends "model": "anthropic/claude-sonnet-4", the agent uses that model. Controlled by a config flag.

Configuration

# In config.yaml
api_server:
  enabled: true
  port: 8642
  host: "127.0.0.1"        # localhost only by default
  key: "your-secret-key"   # or via API_SERVER_KEY env var
  allow_model_override: false  # let clients choose the model
  max_concurrent: 5         # max simultaneous requests

Environment variables:

API_SERVER_ENABLED=true
API_SERVER_PORT=8642
API_SERVER_HOST=127.0.0.1
API_SERVER_KEY=your-secret-key

Implementation Plan

Phase 1: MVP (non-streaming) — PR

1. gateway/platforms/api_server.py — new adapter

   • aiohttp.web server with endpoints:
     • POST /v1/chat/completions — Chat Completions API (universal compat)
     • POST /v1/responses — Responses API (server-side state, tool preservation)
     • GET /v1/models — list available models
     • GET /health — health check
   • Bearer token auth middleware
   • Non-streaming responses (run agent, return full result)
   • Chat Completions: stateless, messages array is the conversation
   • Responses API: server-side conversation storage via previous_response_id
     • Store full internal conversation (including tool calls) keyed by response ID
     • On subsequent requests, reconstruct full context from stored chain
   • Frontend system prompt layered on top of hermes-agent's core prompt

2. gateway/config.py — add Platform.API_SERVER enum + config

3. gateway/run.py — register adapter in _create_adapter()

4. Tests in tests/gateway/test_api_server.py

Phase 2: SSE Streaming

1. Add response streaming to both endpoints

   • Chat Completions: choices[0].delta.content SSE format
   • Responses API: semantic events (response.output_text.delta, etc.)
   • Run agent in thread, collect output via callback queue
   • Handle client disconnect (cancel agent)

2. Add stream_callback parameter to AIAgent.run_conversation()

Phase 3: Enhanced Features

1. Tool call transparency mode (opt-in)
2. Model passthrough/override
3. Concurrent request limiting
4. Usage tracking / rate limiting
5. CORS headers for browser-based frontends
6. GET /v1/responses/{id} — retrieve stored response
7. DELETE /v1/responses/{id} — delete stored response

Files Changed

Compatibility Matrix

Once implemented, hermes-agent works as a drop-in backend for: