plano/demos/llm_routing/model_routing_service

Model Routing Service Demo

This demo shows how to use the /routing/v1/* endpoints to get routing decisions without proxying requests to an LLM. The endpoint accepts standard LLM request formats and returns which model Plano's router would select.

Setup

Make sure you have Plano CLI installed (pip install planoai or uv tool install planoai).

export OPENAI_API_KEY=<your-key>
export ANTHROPIC_API_KEY=<your-key>

Start Plano:

cd demos/llm_routing/model_routing_service
planoai up config.yaml

Run the demo

./demo.sh

Endpoints

All three LLM API formats are supported:

Endpoint	Format
POST /routing/v1/chat/completions	OpenAI Chat Completions
POST /routing/v1/messages	Anthropic Messages
POST /routing/v1/responses	OpenAI Responses API

Example

curl http://localhost:12000/routing/v1/chat/completions \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-4o-mini",
    "messages": [{"role": "user", "content": "Write a Python function for binary search"}]
  }'

Response:

{
    "model": "anthropic/claude-sonnet-4-20250514",
    "route": "code_generation",
    "trace_id": "c16d1096c1af4a17abb48fb182918a88"
}

The response tells you which model would handle this request and which route was matched, without actually making the LLM call.

Session Pinning

Send an X-Session-Id header to pin the routing decision for a session. Once a model is selected, all subsequent requests with the same session ID return the same model without re-running routing.

# First call — runs routing, caches result
curl http://localhost:12000/routing/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "X-Session-Id: my-session-123" \
  -d '{
    "model": "gpt-4o-mini",
    "messages": [{"role": "user", "content": "Write a Python function for binary search"}]
  }'

Response (first call):

{
    "model": "anthropic/claude-sonnet-4-20250514",
    "route": "code_generation",
    "trace_id": "c16d1096c1af4a17abb48fb182918a88",
    "session_id": "my-session-123",
    "pinned": false
}

# Second call — same session, returns cached result
curl http://localhost:12000/routing/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "X-Session-Id: my-session-123" \
  -d '{
    "model": "gpt-4o-mini",
    "messages": [{"role": "user", "content": "Now explain merge sort"}]
  }'

Response (pinned):

{
    "model": "anthropic/claude-sonnet-4-20250514",
    "route": "code_generation",
    "trace_id": "a1b2c3d4e5f6...",
    "session_id": "my-session-123",
    "pinned": true
}

Session TTL and max cache size are configurable in config.yaml:

routing:
  session_ttl_seconds: 600      # default: 600 (10 minutes)
  session_max_entries: 10000    # default: 10000

Without the X-Session-Id header, routing runs fresh every time (no breaking change).

Demo Output

=== Model Routing Service Demo ===

--- 1. Code generation query (OpenAI format) ---
{
    "model": "anthropic/claude-sonnet-4-20250514",
    "route": "code_generation",
    "trace_id": "c16d1096c1af4a17abb48fb182918a88"
}

--- 2. Complex reasoning query (OpenAI format) ---
{
    "model": "openai/gpt-4o",
    "route": "complex_reasoning",
    "trace_id": "30795e228aff4d7696f082ed01b75ad4"
}

--- 3. Simple query - no routing match (OpenAI format) ---
{
    "model": "none",
    "route": null,
    "trace_id": "ae0b6c3b220d499fb5298ac63f4eac0e"
}

--- 4. Code generation query (Anthropic format) ---
{
    "model": "anthropic/claude-sonnet-4-20250514",
    "route": "code_generation",
    "trace_id": "26be822bbdf14a3ba19fe198e55ea4a9"
}

--- 7. Session pinning - first call (fresh routing decision) ---
{
    "model": "anthropic/claude-sonnet-4-20250514",
    "route": "code_generation",
    "trace_id": "f1a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6",
    "session_id": "demo-session-001",
    "pinned": false
}

--- 8. Session pinning - second call (same session, pinned) ---
    Notice: same model returned with "pinned": true, routing was skipped
{
    "model": "anthropic/claude-sonnet-4-20250514",
    "route": "code_generation",
    "trace_id": "a9b8c7d6e5f4a3b2c1d0e9f8a7b6c5d4",
    "session_id": "demo-session-001",
    "pinned": true
}

--- 9. Different session gets its own fresh routing ---
{
    "model": "openai/gpt-4o",
    "route": "complex_reasoning",
    "trace_id": "1a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6d",
    "session_id": "demo-session-002",
    "pinned": false
}

=== Demo Complete ===