colibrì 🐦

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. Measured 2.00 tokens/forward (100% acceptance) on structured text. Lossless: output identical to greedy.
• Quantization kernels: int8 / packed int4 / packed int2, per-row scales, AVX2, dequant-on-use. Packing validated bit-identical to the int8 container.
• 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)

metric	value
model on disk (int4 container)	~370 GB
resident RAM (dense, int4)	9.9 GB
load time	~30 s
peak RSS during chat	~20 GB (auto-capped)
cold decode cost	~11 GB disk reads/token (75 layers × 8 experts)
disk ceiling (VHDX random)	~1 GB/s → ~0.05–0.1 tok/s cold
MTP speculation	2.0 tok/forward measured

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.

Quick start

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

# convert the model (resumable, needs ~400 GB free on a real ext4/NVMe path):
./coli convert                  # from zai-org/GLM-5.2-FP8

# chat (RAM budget and expert cache size itself automatically):
COLI_MODEL=/path/to/glm52_i4 ./coli chat

Useful knobs (env or flags): --topp 0.7 adaptive expert top-p (30–40% less disk), --ngen N max tokens, STATS=f/PIN=f PIN_GB=g record expert usage then pin the hottest in RAM, THINK=1 enable GLM-5.2's reasoning block, DRAFT=n MTP draft depth, TF=1 teacher-forcing validation.

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/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
*.py             research scripts (cost model, trace analysis, py engine)

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.