# Architecture: LLM Backends

> How Cortex selects and talks to AI models.
> Last updated: 2026-04-27 (V2 schema)

---

## Providers

Cortex supports four model types, each dispatched differently:

| Type | Auth | Use |
|---|---|---|
| `claude_cli` | OAuth token from `~/.claude/.credentials.json` | Chat, persona responses |
| `gemini_cli` | Gemini CLI credentials | Chat fallback / explicit selection |
| `gemini_api` | API key from registry account or `.env` | Orchestrator tool loop |
| `local_openai` | API key per host in model registry | Open WebUI, Ollama, OpenRouter, LiteLLM, etc. |

---

## Backend Selection

### Default: Role-Based Routing (Auto)

When no explicit backend is selected, Cortex routes to the model configured for the
request's **role** in the user's model registry. Roles: `chat`, `orchestrator`, `distill`,
`coder`, `research` (extensible via `DEFINED_ROLES` in `.env`).

Resolution order for a role:
1. User registry: `roles[role].primary → backup_1 → backup_2 → backup_3 → backup_4`
2. `.env` role default: `ROLE_CHAT=claude_cli`, `ROLE_DISTILL=claude_cli`, etc.
3. Hardcoded last-resort: `chat/distill/coder → claude_cli`, `orchestrator/research → gemini_api`

### Explicit Override

The UI backend toggle cycles: **auto → claude → gemini → local → auto**

- **auto** (default): role-based routing as above
- **claude / gemini / local**: bypasses role routing; forces that backend type
- The toggle will be redesigned in Phase 3 to cycle through chat role slots (Primary / Backup 1 / Backup 2)

**Fallback chain** (automatic, only when no explicit registry entry exists):
```
claude  → gemini
gemini  → claude
local   → claude
```
When a model is explicitly configured in the registry, errors surface immediately — no silent fallback.

Each response shows a model tag (bottom-right of the message bubble) with the model label and host.

---

## Model Registry — V2 Schema

Per-user configuration stored in `home/{user}/model_registry.json`.

Managed at **Settings → Models** (`/settings/models`). Full provider UI coming in Phase 2.

```json
{
  "version": 2,

  "providers": {
    "anthropic": {
      "credentials": [
        {"id": "cli", "label": "Claude CLI (OAuth)", "type": "cli"}
      ]
    },
    "google": {
      "accounts": [
        {"id": "a1b2", "label": "One Sky IT", "api_key": "AIza..."}
      ]
    }
  },

  "hosts": [
    {
      "id": "abc123",
      "label": "Gaming Laptop",
      "api_url": "http://192.168.x.x:3000",
      "api_key": "",
      "host_type": "openwebui"
    }
  ],

  "models": [
    {
      "id": "m1",
      "type": "claude_cli",
      "label": "Sonnet 4.6 (CLI)",
      "model_name": "claude-sonnet-4-6",
      "provider": "anthropic",
      "credential_id": "cli",
      "context_k": 200,
      "tags": ["chat", "persona"]
    },
    {
      "id": "m2",
      "type": "gemini_api",
      "label": "Gemini 2.5 Flash (OSIT)",
      "model_name": "gemini-2.5-flash",
      "provider": "google",
      "account_id": "a1b2",
      "context_k": 1000,
      "tags": ["orchestrator", "research"]
    },
    {
      "id": "m3",
      "type": "local_openai",
      "label": "Gemma 4 E4B",
      "model_name": "gemma4:e4b",
      "provider": "local",
      "host_id": "abc123",
      "context_k": 72,
      "tags": ["fast", "local"]
    }
  ],

  "roles": {
    "chat":         {"primary": "m1", "backup_1": "m2", "backup_2": "m3"},
    "orchestrator": {"primary": "m2", "backup_1": "m3"},
    "distill":      {"primary": "m1"}
  }
}
```

### host_type (local hosts)

| `host_type` | Chat endpoint | Models endpoint | Use for |
|---|---|---|---|
| `openwebui` (default) | `POST {url}/api/chat/completions` | `GET {url}/api/models` | Open WebUI, Ollama |
| `openai` | `POST {url}/chat/completions` | `GET {url}/models` | OpenRouter, LiteLLM, Anthropic-compat |

Set `api_url` to the base path before `/chat/completions`:
- OpenRouter: `https://openrouter.ai/api/v1`

### Built-in model IDs

Always resolvable without a user-created registry entry. Used as role defaults.

| ID | Type | Notes |
|---|---|---|
| `claude_cli` | `claude_cli` | Model from `DEFAULT_MODEL` in `.env` |
| `gemini_cli` | `gemini_cli` | Gemini CLI subprocess |
| `gemini_api` | `gemini_api` | Model from `ORCHESTRATOR_MODEL` in `.env`; key from `GEMINI_API_KEY` |

### V1 → V2 migration

Automatic on first load. Changes:
- Adds `providers` section (Anthropic CLI credential + empty Google accounts)
- Migrates `gemini_api_key` from `auth.json` → `providers.google.accounts[0]`
- All existing hosts, models, and role assignments are preserved

---

## Claude Backend (`_claude()`)

Runs `claude --print --no-session-persistence --output-format text` as a subprocess.

- System prompt passed via `--system-prompt`
- Conversation history formatted as `<conversation>` block
- Token read live from `~/.claude/.credentials.json` on every call — never uses the
  env var, which goes stale after `claude auth login`
- Model override via `--model` flag when `model_name` is set in the registry entry

Timeout: `TIMEOUT_CLAUDE=60` seconds (`.env`)

---

## Gemini CLI Backend (`_gemini()`)

Runs `gemini --output-format text --extensions "" -p <prompt>` as a subprocess.

- `--extensions ""` disables all MCP extensions — prevents child processes keeping pipes open
- `start_new_session=True` puts the process in its own group for clean `os.killpg` on timeout
- Output is cleaned to strip CLI noise (loading messages, retry notices, quota warnings)

Timeout: `TIMEOUT_GEMINI=120` seconds (`.env`)

---

## Local Backend (`_local()`)

HTTP POST to an OpenAI-compatible endpoint. Model config is resolved via the model registry.

```python
# host_type "openwebui":  POST {api_url}/api/chat/completions
# host_type "openai":     POST {api_url}/chat/completions
```

Timeout: `TIMEOUT_LOCAL=300` seconds (`.env`) — local models may need to load from disk.

---

## Gemini API (Orchestrator)

Used by `orchestrator_engine.py` for the ReAct tool loop. Not used for general chat.

API key resolution order:
1. `api_key` embedded in the resolved orchestrator model config (V2 registry with `account_id`)
2. `get_user_gemini_key(user)` — reads from `auth.json` (legacy, kept for compat)
3. `GEMINI_API_KEY` in `.env` (server default)

---

## Distillation

Memory distillation uses `role="distill"`. Configure via Model Registry → Role Assignments.

`.env` override: `ROLE_DISTILL=claude_cli` (default).

---

## Future: Phase 3 — Backend Toggle Redesign

The `claude → gemini → local` toggle will be replaced with a slot toggle that cycles
through the chat role's configured models (Primary → Backup 1 → Backup 2), showing
the actual model label. See `DESIGN__Model_Registry_V2.md`.

---

## Code locations

| File | Responsibility |
|---|---|
| `cortex/llm_client.py` | `complete()` — routing, dispatch, fallback |
| `cortex/model_registry.py` | Per-user registry CRUD and resolution (V2) |
| `cortex/routers/local_llm.py` | Settings UI routes + `/api/models/role` AJAX |
| `cortex/routers/chat.py` | `_backend_label()`, `fallback_used` flag |
| `cortex/routers/orchestrator.py` | Engine selection, Gemini API key resolution |
| `cortex/config.py` | `ROLE_*` env defaults, `DEFINED_ROLES`, `PRIMARY_BACKEND` |