# llama.cpp Router Mode on Apple Silicon

**Single GPU, two models, zero contention — from 12 t/s to 132 t/s**

A practical guide to running multiple LLMs on one Apple Silicon Mac using `llama-server` router mode, achieving full GPU bandwidth for each model with automatic LRU eviction.

## The Problem

Running two `llama-server` processes on the same GPU causes severe bandwidth contention:

```
Two separate servers (before):
  35B MoE:  23 t/s  ← -75% from potential
  27B dense: 16 t/s  ← -63% from potential
```

Both models stay permanently loaded, permanently competing for GPU memory bandwidth.

## The Solution

A single `llama-server` with `--models-max 1` evicts the idle model from GPU memory, giving full bandwidth to whichever model is active:

```
Router mode (after):
  35B MoE:  132 t/s  ← 5.7x faster
  27B dense:  48 t/s  ← 3.0x faster
```

## Quick Start

```bash
# 1. Create model symlinks
mkdir -p ~/.hermes/models-router
ln -sf /path/to/model1.gguf ~/.hermes/models-router/
ln -sf /path/to/model2.gguf ~/.hermes/models-router/

# 2. Create per-model INI preset
cat > ~/.hermes/llama-models.ini << 'EOF'
[*]
flash-attn = on
cache-type-k = q4_0
cache-type-v = q4_0
batch-size = 512
ubatch-size = 128
spec-type = draft-mtp
spec-draft-n-max = 3

[model.Model1]
threads = 14

[model.Model2]
threads = 10
EOF

# 3. Launch router
llama-server \
  --models-dir ~/.hermes/models-router \
  --models-max 1 \
  --models-preset ~/.hermes/llama-models.ini \
  --host 0.0.0.0 --port 8085 \
  -ngl 99 -c 131072 --mlock \
  --metrics
```

## Speed Results (M5 Max 40-core, 128GB)

| Model | Two Servers | Router Mode | Gain |
|-------|-------------|-------------|------|
| Qwen3.6-35B-A3B-Q8_0 (MoE) | 23 t/s | 132 t/s | **5.7x** |
| Qwen3.6-27B-Q8_0 (dense) | 16 t/s | 48 t/s | **3.0x** |

Trade-off: ~3-4s model load time when switching models.

## Hardware

- **Chip:** Apple M5 Max (40 GPU cores, 614 GB/s bandwidth)
- **RAM:** 128 GB Unified Memory
- **Software:** llama.cpp b9910+, launchd, Hermes Agent

## Contents

- `docs/` — Full optimization journey with benchmarks at each step
- `configs/` — Launchd plist, INI preset, utility scripts
- `benchmarks/` — Before/after speed comparison data

## License

MIT — use it, share it, productize it.