Tiny engine, immense model. Run GLM-5.2 (744B-parameter MoE) on a consumer machine with ~25 GB of RAM — in pure C, with zero dependencies, by streaming experts from disk.

$ ./coli chat
  🐦 colibrì v1.0 — GLM-5.2 · 744B MoE · int4 · streaming CPU
  ✓ pronto in 32s · residente 9.9 GB
  › ciao!
  ◆ Ciao! 😊 Come posso aiutarti oggi?

The idea

A 744B Mixture-of-Experts model activates only ~40B parameters per token — and only ~11 GB of those change from token to token (the routed experts). So:

• the dense part (attention, shared experts, embeddings — ~17B params) stays resident in RAM at int4 (~9.9 GB);
• the 21,504 routed experts (75 MoE layers × 256 experts + the MTP head, ~19 MB each at int4) live on disk (~370 GB) and are streamed on demand, with a per-layer LRU cache, an optional pinned hot-store, and the OS page cache as a free L2.

The engine is a single C file (c/glm.c, ~1,300 lines) plus small headers. No BLAS, no Python at runtime, no GPU.

What's implemented

• Faithful GLM-5.2 (glm_moe_dsa) forward — validated token-exact against a transformers oracle (teacher-forcing 32/32, greedy 20/20 on a tiny-random model with the real architecture).
• MLA attention (q/kv-LoRA, interleaved partial RoPE) with compressed KV-cache: 576 floats/token instead of 32,768 (57× smaller — GLM-5.2 has 64 heads and no GQA).
• DeepSeek-V3-style sigmoid router (noaux_tc, routed_scaling_factor), shared expert, first-3-dense layers.
• Native MTP speculative decoding — GLM-5.2's own multi-token-prediction head (layer 78) drafts tokens that the main model verifies in one batched forward. The head must be int8 (the converter does this by default): at int4 draft acceptance collapses to 0–4% and speculation never engages; at int8 it's 39–59% acceptance, 2.2–2.8 tokens/forward (community-measured, #8). Lossless — and stays lossless under sampling via rejection sampling. Honest caveat from the same measurement: on a cold cache each verified draft routes to extra experts (~660 → ~1100 expert-loads/token), so speculation can be a net time loss until the cache/pin warms up — the adaptive guard and DRAFT=0 are there for that.
• True sampling — temperature + nucleus, defaults tuned for int4 reality (0.7 / 0.90; the official 1.0 / 0.95 samples quantization noise from the tail).
• Integer-dot kernels (Q8_0-style int8 activations, AVX2 maddubs): int8 matmuls 1.4–2.5× faster (119 GFLOP/s measured), int4 1.8× in batch — routing decided per shape by measurement (int4 single-row stays f32: it measured slower).
• MLA weight absorption (DeepSeek trick) for decode: no per-token k/v reconstruction — the query absorbs kv_b, context is projected after attention. Validated exact: TF 32/32 and generation 20/20 with absorption forced everywhere.
• Async expert readahead: while one block of experts is being multiplied, the kernel is already reading the next (WILLNEED).
• Quantization kernels: int8 / packed int4 / packed int2, per-row scales, AVX2, dequant-on-use. Packing validated bit-identical to the int8 container.
• DSA sparse attention: in progress — the lightning-indexer weights (a ~108 GB extraction from the FP8 repo, --indexer converter mode) are downloading; the indexer forward lands next. Until then attention is dense and exact for contexts ≤ 2048 tokens.
• Batch-union MoE: in prefill (and MTP verification), each unique expert of the batch is read once and applied to every position that routes to it.
• Byte-level BPE tokenizer in C (GPT-2-style with Unicode-property regex, 320k merges).
• RAM safety: the expert cache is auto-sized from MemAvailable at startup — an honest peak projection (working set, KV, MTP row, reconstruction buffers) so the kernel OOM-killer never fires.
• Offline FP8→int4 converter (c/convert_fp8_to_int4.py): downloads one shard at a time (~5 GB), dequants (128×128 block scales), requantizes to the engine's container, deletes the shard — the 756 GB FP8 checkpoint never needs to exist on disk at once. Resumable.

Honest numbers (WSL2, 12 cores, 25 GB RAM, NVMe via VHDX)

This is not fast. It is a 744B frontier-class model answering correctly on a machine that costs less than one H100 fan. Warm cache, pinned hot experts and MTP push the useful-response latency down considerably; the physics of the disk does the rest.

SSD Wear Warning

Cold starts are heavy on random reads (~11 GB/token). Reads themselves are safe, but the OS page cache can generate writes. Heavy use may accelerate wear on cheaper SSDs. Use with caution and monitor your drive health.

Download the model

A pre-converted GLM-5.2 int4 model for colibrì is available on Hugging Face:

https://huggingface.co/jlnsrk/GLM-5.2-colibri-int4

Download the repository and point COLI_MODEL to its directory:

COLI_MODEL=/path/to/GLM-5.2-colibri-int4 ./coli chat

This skips the FP8 → int4 conversion step entirely.

Thanks DatPat for your help!

Quick start

cd c
./setup.sh                      # checks gcc/OpenMP, builds, self-tests

# ONE command does everything model-side: downloads GLM-5.2-FP8 shard by shard
# (never needs the full 756 GB at once), converts to the int4 container, then
# converts the MTP head for speculative decoding. Resumable at any point.
# Conversion (only) needs python with: pip install torch safetensors huggingface_hub numpy
./coli convert --model /nvme/glm52_i4     # ~400 GB free on a real ext4/NVMe path

# chat — RAM budget, expert cache and MTP are all detected automatically:
COLI_MODEL=/nvme/glm52_i4 ./coli chat

The engine at runtime is pure C — python is only used by the one-time converter.

Useful knobs (env or flags): --temp T token sampling temperature (default 0.7 + nucleus 0.90 — tuned for int4; 0 = greedy), --topp 0.7 adaptive expert top-p (30–40% less disk), --ngen N max tokens per answer (:piu in chat continues a truncated one), AUTOPIN=0 disable the learning cache's auto-pin, THINK=1 enable GLM-5.2's reasoning block, DRAFT=n MTP draft depth, TF=1 teacher-forcing validation.

The learning cache: the engine records which experts your usage actually routes to (.coli_usage next to the model, updated every turn) and at startup automatically pins the hottest ones in spare RAM. colibrì literally gets faster the more you use it.

Got a better machine? Try it — here's what to expect

colibrì was built on deliberately humble hardware (12 cores, 25 GB RAM, NVMe behind a WSL2 VHDX that caps random reads at ~1 GB/s). Every one of those constraints is a knob your machine can turn up. The engine needs: Linux (or WSL2), gcc with OpenMP, AVX2, ≥16 GB RAM, and the ~370 GB int4 model on a local NVMe (ext4 — never a network/9p mount).

How to test it, in order:

cd c && ./setup.sh                 # build + architecture self-test (expects 32/32)

# 1) measure YOUR disk the way the engine uses it (parallel 19 MB random reads):
gcc -O2 -fopenmp iobench.c -o iobench
./iobench /path/to/glm52_i4/out-00069.safetensors 19 64 8 0   # buffered, 8 threads
./iobench /path/to/glm52_i4/out-00069.safetensors 19 64 8 1   # O_DIRECT

# 2) chat; watch the per-turn stats line (tok/s, expert hit-rate, RSS):
COLI_MODEL=/path/to/glm52_i4 ./coli chat

# 3) record expert usage, then pin the hottest experts in your spare RAM:
STATS=stats.txt ./coli chat
PIN=stats.txt PIN_GB=20 ./coli chat        # scale PIN_GB to your free RAM

# 4) quality benchmarks (MMLU/HellaSwag/ARC):
./coli bench

Back-of-envelope predictions (decode is disk-bound: a cold token costs ~11.4 GB of expert reads; MTP speculation roughly halves the effective cost once the cache is warm; RAM turns cold reads into free cache hits):

These are estimates, not measurements — if you run colibrì on serious hardware, please open an issue with your numbers: real datapoints from better machines are exactly what this project needs next.

Community benchmarks (measured)

Real numbers from real machines, stock build (setup.sh, gcc 13), greedy decoding, --ngen 32, MTP active:

Takeaways: with 24 GB of RAM the engine auto-caps the expert cache to 2 slots/layer, so decode stays cold even on a disk 2–2.7× faster than the dev box — on small-RAM machines the RAM cap, not the disk, is the binding constraint, exactly as the table above predicts; --topp 0.7 alone bought a clean 1.6× end-to-end speedup. The M5 Max datapoint lands right on the table's second row: ~1 tok/s of a 744B model on a laptop SSD — and its 14 GB/s disk shifts the bottleneck back to RAM budget and kernels.

Quality benchmark — help wanted

We have never measured how much the int4 quantization costs in accuracy — the harness is built and wired, but scoring is one forward per answer option, and on the dev box's ~1 GB/s disk a full run takes the better part of a day. This is the single most valuable thing a faster machine can contribute. The code is here and ready; one command runs it end to end (it auto-downloads the datasets on first use):

cd c
./coli bench                                   # hellaswag, arc_challenge, mmlu — 40 questions each
./coli bench hellaswag --limit 200             # one task, more questions
./coli bench mmlu arc_challenge --ram 100      # pick tasks, set a RAM budget

It prints per-task accuracy (log-likelihood scoring, EleutherAI-harness style). Published full-precision GLM-5.2 scores on these tasks sit around 85–95%; if our int4 container lands within a few points, the quantization is validated — if it doesn't, we know to invest in mixed / grouped-scale quantization. If you have the hardware to run this, please open an issue with the numbers — it's the measurement the project is missing.

Supporting the project

colibrì is a one-person project, written and tested entirely on a 12-core laptop with 25 GB of RAM — the numbers above are the ceiling of what I can measure at home. If this project is useful or interesting to you and you'd like to support its development (better test hardware translates directly into a faster engine for everyone: real NVMe scaling data, bigger pinned caches, int2/int3 quality sweeps on real benchmarks), you can:

• ⭐ star the repo and share it;
• 🐛 open issues with benchmark numbers from your hardware;
• 💬 reach out via GitHub issues if you'd like to sponsor development or donate hardware.

Every contribution, from a datapoint to a disk, moves the ceiling.

Repo layout

c/glm.c          the engine (GLM-5.2 forward, streaming MoE, MTP, serve mode)
c/st.h           safetensors reader: pread + fadvise, no mmap (RSS stays flat)
c/tok.h          byte-level BPE tokenizer in C
c/coli           CLI: chat / run / bench / convert / info
c/iobench.c      parallel disk microbenchmark (measures what the engine feels)
c/convert_fp8_to_int4.py   disk-safe FP8 → int4 converter
c/make_glm_oracle.py       tiny-random oracle generator for validation
c/olmoe.c        stage-A engine (OLMoE), first validation target

Why "colibrì"

The hummingbird weighs a few grams, hovers in place, and visits a thousand flowers a day. This engine keeps a 744-billion-parameter giant alive on hummingbird rations: 25 GB of RAM, twelve CPU cores, and a lot of disk patience.

License

Apache 2.0. GLM-5.2 weights are released by Z.ai under MIT.