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Tiny engine, immense models — run large MoE LLMs (gpt-oss, Mixtral, Qwen3-MoE) on ordinary machines by streaming experts from disk. OpenAI-compatible server with tool calling + hybrid cloud relay; CPU, Apple Silicon & CUDA (MLX).

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# midge

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**Tiny engine, immense models.** Run 100B+ mixture-of-experts LLMs on an
ordinary CPU machine with a few GB of RAM, by keeping only the dense trunk
resident and streaming the routed experts from disk.

A small spec-driven C engine plus a converter, so one binary runs **any
model in the MoE-transformer family it implements** — today that's
**gpt-oss**, **Mixtral-style**, and **Qwen3-MoE-style** models (GQA ·
RoPE/YaRN · top-k softmax router, with clamped/plain SwiGLU, QK-norm, and
`norm_topk_prob` variants). Point `midge check <any-hugging-face-repo>` at
a model and it tells you *before* you download whether this machine can
run it — and names the reason if it can't (e.g. MLA or shared experts,
which aren't implemented). Adding a family is a spec plus a tensor map,
not a new engine.

It also does more than run models locally:

* an **OpenAI-compatible server** with streaming, a session prefix cache,
  and **tool / function calling** — so agent frameworks (OpenClaw,
  Hermes-style, anything that speaks the OpenAI API) work against it;
* a **hybrid mode** that can relay permitted requests to a faster
  upstream you choose — a cloud API, or your own GPU box on the LAN — at
  that upstream's speed, and transparently fall back to the local model
  when it's unavailable, with per-request privacy pinning;
* a **web onboarding UI** (`./midge ui`) that searches Hugging Face,
  downloads, converts, builds, and opens a chat panel with zero terminal
  steps.

Double-click installers (.dmg / .zip / .tar.gz) are attached to each
[release](https://github.com/drmihirbrahme/midge/releases); see
[docs/INSTALL.md](docs/INSTALL.md). Or clone and `./install.sh` on any
platform.

midge began from [colibri](https://github.com/JustVugg/colibri), which
proved disk-streamed experts on GLM; it has since grown into its own
engine, converter, format, server, and toolchain.

```
model            experts on disk   resident RAM (dense+KV)   cold IO/token
gpt-oss-120b     ~60 GiB (MXFP4)   ~2.5 GiB                  ~1.9 GiB
gpt-oss-20b      ~10 GiB (MXFP4)   ~2.0 GiB                  ~1.3 GiB
```

A 75 GB disk and 8 GB of RAM are enough for the 120B model. That is the
whole point.

Two engines share one converted model directory:

* **`midged` (C)** — Linux/POSIX, mmap + page-cache expert streaming.
* **`midge-mlx` (Python)** — Apple Silicon via [MLX](https://github.com/ml-explore/mlx);
  the dense trunk sits in unified memory (requantized to 4/8-bit affine on
  load) and experts stream from disk through a byte-budgeted LRU straight
  into MLX's native quantized kernels — the container's MXFP4 and int4
  blobs are consumed **as-is** (`mode="mxfp4"` / affine-int4 with
  `biases = −8·scales`), no re-conversion, verified bit-for-bit.

## How it works

* **The dense trunk stays hot.** Embeddings, attention, router and norms
  (~2 GiB quantized at int8) are mmap'd and touched every token, so the OS
  keeps them resident.
* **Experts live on disk.** All expert FFNs sit in one big `experts.midge`
  file at deterministic offsets, mmap'd with `MADV_RANDOM`. Each token
  touches only `top_k × n_layers` experts (e.g. 4 × 36 ≈ 1.9 GiB for
  120b). The OS page cache *is* the expert cache: frequently-routed
  experts stay in whatever RAM you have, cold ones are read on demand,
  and memory pressure never OOMs you because the pages are file-backed
  and clean.
* **Usage-aware warmup.** The engine records per-expert routing counts in
  `usage.bin`; `--preload-gb N` pre-faults the N hottest gigabytes at
  startup.
* **MXFP4 kept intact.** gpt-oss ships 4-bit MXFP4 experts; the converter
  transcodes them losslessly (nibbles copied verbatim, e8m0 scales
  rewritten exactly as f16), so there is no requantization loss and no
  giant intermediate file — conversion streams shard-by-shard and needs
  only ~1 shard of scratch space.

## Performance

The kernels are runtime-dispatched: AVX2+FMA on x86 (≈8–9× the scalar
fallback — measured 3.98 vs 0.48 GB/s/core on the same machine; scalar
remains for ARM and can be forced with `MIDGE_NO_SIMD=1`). Threads scale
across cores via OpenMP. Measured on a single cloud core with real
gpt-oss expert dimensions: 12.2 tok/s warm on a 4-layer slice — which
extrapolates to roughly **1–1.5 tok/s** for the full 36-layer 120b on
one core, compute-side, and several× that on desktop core counts, where
the real ceiling becomes cache hit rate and disk. Cold decoding is
IO-bound: ≈ `disk_MB/s ÷ 1900` tok/s for 120b, so NVMe and
`--preload-gb` matter. `./midge check` measures *your* kernel, disk and
RAM and prints estimates for your machine. Prompt prefill is batched
(expert-major), which matters exactly when it should: 3.3× measured
under memory pressure — the regime a bigger-than-RAM model lives in. Cold decoding issues
advisory prefetch for routed experts so disk readahead can overlap
compute (a large effect pre-SIMD, neutral on a single fast core —
see docs/SPEED.md for the honest numbers).

**Hybrid mode**: point `midge serve` at any OpenAI-compatible upstream
(`--upstream URL --route auto`) and permitted requests run at literal
cloud speed while everything falls back to the local model the moment
the upstream is down — per-request `"midge_route": "local"` keeps
sensitive calls on-device, and every response is tagged with who served
it. Details, measurements, and the speed roadmap (batched prefill,
speculative decoding, LAN expert swarm): [docs/SPEED.md](docs/SPEED.md).

Honest framing: this is a read-the-weights-every-token design. It will
not race a datacenter GPU serving the same model — its job is running
models that don't fit your machine at all. For latency-sensitive agent
use, prefer **gpt-oss-20b** (much gentler IO, higher cache hit rates),
`--reasoning low`, streaming, and the session prefix cache (on by
default in `midge serve`). On Apple Silicon or NVIDIA GPUs the MLX
backend uses MLX's optimized kernels and is faster still.

## Installation

```bash
git clone https://github.com/drmihirbrahme/midge && cd midge
./install.sh
```

The installer checks your toolchain, installs the Python dependencies
(`requirements.txt`), builds the engine, and runs a smoke test.
Prerequisites by OS:

* **Ubuntu/Debian**: `sudo apt install build-essential python3-pip git`
* **macOS**: `xcode-select --install` — the C engine builds
  single-threaded there (Apple's clang lacks OpenMP); Apple Silicon
  users should use the MLX engine instead: `pip install mlx`, then
  `./midge-mlx` / `--backend mlx`
* **NVIDIA GPU (Linux)**: additionally `pip install "mlx[cuda]"`

Manual install is just `pip install -r requirements.txt && make`.
Python 3.9+ required.

## Usage

### The easy way: the interface

```bash
./midge ui
```

opens a local web app that handles everything: pick a model from the
catalog (storage needs are shown against your free disk), watch the
Hugging Face download and conversion stream by with live progress, the
engine builds itself at the end, and a chat panel opens — backed by the
same OpenAI-compatible server agents connect to. Interrupted downloads
resume with one click. New models are added by dropping an entry into
`specs/catalog.json` (plus a spec), which is the base for upcoming
model choices.

Everything below is the same pipeline as individual commands.

### 0. Will it run? (any Hugging Face model)

```bash
./midge check mistralai/Mixtral-8x7B-Instruct-v0.1
./midge check Qwen/Qwen3-30B-A3B      # any repo id or local path
```

fetches only the model's `config.json`, decides whether the
architecture is inside the engine's family (with specific reasons when
it isn't — "MLA is not implemented", not a shrug), then measures *this
device* — the real engine kernel's throughput, disk read speed, free
disk, available RAM — and prints a verdict with honest tok/s estimates:

```
model    openai/gpt-oss-120b  ·  arch: gpt-oss
needs    62.3 GB disk (peaks 68.3 GB converting) · 3.0 GB resident RAM at ctx 8192
device   210 GB disk free · 24.1/32.0 GB RAM available · 8 cores
measured kernel 3.1 GB/s · disk 2350 MB/s
estimate ~1.2 tok/s warm · ~1.1 tok/s cold (1.88 GB read/token cold)
verdict  ✓ can run
```

Exit code 0 = can run, 1 = can't — usable in scripts. The same check
lives in the web UI's "any Hugging Face model" box, and as a library
(`from doctor import analyze`). Supported families today: **gpt-oss**,
**Mixtral-style**, and **Qwen3-MoE-style** (plain SwiGLU, QK-norm,
`norm_topk_prob` routers) — all three validated against the NumPy
reference in CI. Architectures with MLA, shared experts, or sigmoid
routers are refused with the reason named.

### 1. Convert a checkpoint

```bash
# straight from the Hub — shards are downloaded one at a time and
# deleted after processing, so you never need the full checkpoint on disk
./midge convert openai/gpt-oss-20b models/gpt-oss-20b

# or from a local checkpoint directory
./midge convert /path/to/gpt-oss-120b models/gpt-oss-120b
```

Conversion is resumable — if it is interrupted, run the same command
again and it continues where it stopped. Options: `--experts
mxfp4|q4g32|q8r|f32` (default mxfp4, a lossless transcode for gpt-oss),
`--dense q8r|q4g32|f32` (default q8r), `--keep-shards`.

The output directory contains everything both engines need:
`spec.json`, `dense.midge`, `experts.midge`, `tokenizer.json`.

### 2. Check it fits your machine

```bash
./midge plan models/gpt-oss-120b        # or a spec: specs/gpt-oss-120b.json
```

This prints storage, resident RAM, and cold IO per token, plus
rule-of-thumb throughput for your disk speed.

### 3. Chat

```bash
./midge chat models/gpt-oss-20b
./midge run  models/gpt-oss-20b -p "Explain MoE routing in one paragraph."
```

Flags for both: `--ctx N` context length · `--temp F` / `--topp F`
sampling (temp 0 = greedy) · `--ngen N` max reply tokens ·
`--reasoning low|medium|high` · `--no-analysis` hide the model's
thinking channel · `--system "…"` system prompt · `--preload-gb N`
pre-warm the N hottest gigabytes of experts (routing statistics are
learned in `usage.bin` as you use the model, so this gets better after
the first few chats).

### 4. On a Mac (Apple Silicon)

The MLX engine reads the same model directory — nothing to re-convert:

```bash
./midge-mlx chat models/gpt-oss-20b --cache-gb 4 --dense-bits 8
```

`--cache-gb` is the unified-memory budget for the expert LRU cache;
`--dense-bits 4|8|16|32` requantizes the dense trunk at load time.
Budget roughly: dense (~2 GiB at 8-bit for gpt-oss) + cache + a couple
of GiB for the OS.

### 5. NVIDIA GPUs (CUDA)

The MLX engine is device-agnostic: MLX ships official CUDA wheels for
Linux, and midge's MLX code runs unchanged on them.

```bash
pip install "mlx[cuda]"
./midge-mlx chat models/gpt-oss-20b --device gpu --cache-gb 8
./midge serve models/gpt-oss-20b --backend mlx --device gpu   # API on GPU
```

At startup the engine probes which quantized kernels the active backend
supports and transparently falls back to exact dequantized weights for
any it lacks, so partial backend coverage degrades performance, never
correctness (the fallback path is part of the test suite). Honest
status: developed and validated on MLX's CPU backend — the same code
CUDA executes — but not yet run on physical NVIDIA hardware by the
author. If you have a CUDA box, reports (good or bad) are very welcome.

### 6. Serve an OpenAI-compatible API (for agents and apps)

```bash
./midge serve models/gpt-oss-20b --port 8420 --preload-gb 4
```

exposes `/v1/chat/completions` (streaming and non-streaming),
`/v1/completions` and `/v1/models`, so anything that speaks the OpenAI
API — agent frameworks, IDE assistants, the official client libraries —
can use midge as a local backend:

```python
from openai import OpenAI
client = OpenAI(base_url="http://127.0.0.1:8420/v1", api_key="midge")
r = client.chat.completions.create(model="midge", stream=True,
        messages=[{"role": "user", "content": "hello"}])
```

Notes for slow hardware: use streaming (clients see progress instead of
timing out); one request runs at a time (others queue); the model's
"analysis" channel is returned as `reasoning_content`. The server keeps
the engine's context across requests — an agent loop that appends
messages only pays prefill for the *new* turn, not the whole
conversation, which matters a great deal at CPU prefill speeds. Edited
or divergent histories transparently reset the context.

### Troubleshooting

* **Slow first replies** — cold experts are being read from disk;
  warm-up is normal. Use `--preload-gb` and prefer NVMe.
* **`context full`** — raise `--ctx` (KV memory grows with it; sliding
  layers are capped at the window size regardless).
* **`pip install tokenizers` fails on old Python** — any Python ≥3.9
  with a recent pip works.
* **Conversion ran out of disk** — 120b peaks near ~72 GB during
  conversion; free space or convert 20b first.

## Validation

`make test` runs an end-to-end suite: it generates tiny random checkpoints
in the exact HF gpt-oss format (including the MXFP4 block layout and the
interleaved `gate_up` fusion), converts them with the real converter, and
compares the C engine's logits at every position — plus 24 greedy tokens —
against an independent NumPy implementation, across all supported dtypes
(f32, q8r, q4g32, mxfp4). YaRN RoPE, attention sinks, and the
sliding-window ring KV cache are all inside the tested path. `make
test-mlx` runs the same suite against the MLX engine (MLX ships a CPU
backend, so this runs in CI on Linux too); both engines and both 4-bit
kernel mappings agree with the reference to ~1e-4.

Two additional checks run on your machine against the real weights
(they need torch, so they are not part of CI):

```bash
python3 tools/verify_mxfp4.py openai/gpt-oss-20b        # decode vs transformers, 1 shard
python3 tools/validate_hf.py openai/gpt-oss-20b models/gpt-oss-20b   # logits vs transformers
```

midge's MXFP4 decoding convention (nibble order, FP4 value table, e8m0
scale semantics, block orientation) has additionally been verified
**bit-exactly** against `transformers`' official dequantizer
(`integrations/mxfp4._convert_moe_packed_tensors`) and cross-checked
against OpenAI's reference implementation (`gpt_oss/torch/model.py`) —
same activation clamps, YaRN correction range, sink softmax and
sliding-window semantics.

Honest status: everything above runs on synthetic weights. End-to-end
agreement with `transformers` on the real released checkpoints is a
one-command spot check on your machine (`validate_hf.py`); if it or
`verify_mxfp4.py` fail for you, please open an issue.

## Repository layout

```
midge                 CLI: ui / check / convert / plan / chat / run / serve
midge-mlx             MLX CLI (Apple Silicon & CUDA): chat / run
midged                (built) C engine — token ids in, token ids out
engine/midge.c        the whole engine: spec-driven MoE transformer (+ --bench)
engine/mten.h         .midge container reader (mmap, dtypes, expert layout)
engine/mkern.h        matvec kernels: f32, q8 rows, 4-bit groups (int4/FP4)
engine/mjson.h        small JSON parser
midge_mlx/            MLX engine: unified-memory LRU over the same container
webui/index.html      the onboarding interface (offline, no dependencies)
tools/convert.py      HF checkpoint -> container (streaming, resumable)
tools/doctor.py       `midge check`: compatibility + device-fit verdicts
tools/serve.py        OpenAI-compatible API server (C or MLX backend)
tools/ui.py           interface backend: setup jobs, progress, serve handoff
tools/midgepack.py    codecs + container writers/readers (source of truth)
tools/reference.py    NumPy forward pass (ground truth for tests)
tools/validate*.py    the five test suites (make test / test-mlx / test-server / test-ui)
specs/                model descriptors + catalog.json (the model registry)
docs/                 DESIGN.md · ADDING_MODELS.md
```

## Adding a model

The engine is driven by a JSON spec (see `specs/TEMPLATE.json`): layer
count, GQA shape, per-layer sliding/full attention, YaRN parameters,
router top-k, activation clamps. If your model fits the MoE-transformer
family, you need a spec plus a tensor-name mapping in `tools/convert.py` —
no C changes. Details in [docs/ADDING_MODELS.md](docs/ADDING_MODELS.md).

## Support

Trouble building or loading a model? See [SUPPORT.md](SUPPORT.md) — it
covers the load sequence to expect (and how to tell midge apart from
other tools), plus triage steps. Bugs go to Issues, questions and
real-weight reports to Discussions.

## Author

Dr Mihir Brahme — drmihir@duck.com. Issues and PRs welcome; see
[CONTRIBUTING.md](CONTRIBUTING.md).

## License

Apache-2.0 — see [LICENSE](LICENSE) and [NOTICE](NOTICE).

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