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Tablinum

LFM2.5 1.2B LiteBeam

half a gigabyte, full-size answers

A 1.2B chat model in 542 MiB · scores level with the stock 4.1 bpw quant · measured on 2,500 questions with confidence intervals

LFM2.5 1.2B LiteBeam

params size engine base license

LiteBeam is a hand-built tensor map for LiquidAI/LFM2.5-1.2B-Instruct, not a one-flag quantize. Every sensitive tensor gets a floor; everything else gets the smallest safe rung. The result is a 542 MiB chat model that answers as well as the stock 4.1 bpw quant — which is 5.3% larger — on a 2,500-question multiple-choice benchmark.

If you want a capable, fully offline chat model that costs half a gigabyte of disk, ~660 MiB of VRAM, and runs at 217 tokens/second on a six-gigabyte laptop GPU, this is the file.

Why LiteBeam

1. It is smaller than the stock quant it matches. On 2,500 letter-answerable questions, LiteBeam 3.89 bpw scores 641/2500 and stock llama.cpp Q3_K_M scores 630/2500. Paired, that gap is +0.0044 accuracy, p = 0.60 — a statistical tie — for 5.3% fewer bytes (0.529 GiB vs 0.559 GiB).

2. Sensitive tensors are protected by design. Attention V is pinned at Q5_K on every layer, embeddings at Q4_K or better, and the first and last blocks get a full rung up. That is not what a uniform rule does — it is a deliberate quality floor, applied before the file was measured.

3. Two rungs, both measured end to end. Take 3.89 bpw for the smallest footprint, or 4.80 bpw when you want generation quality that is statistically indistinguishable from the F16 base (p = 0.081). Same model, same prompt format, swap the file.

4. Everything is reproducible. The exact tensor map ships in this repo with its hash, alongside the benchmark's per-item results. Rebuild the file byte-for-byte with the command in Reproduce.

5. It fits beside your other work. Peak VRAM at 2,048 context is 0.659 GiB (3.89 bpw) and 0.783 GiB (4.80 bpw) on a 6 GiB laptop card. On CPU it runs 153 tokens/s prefill, 48 tokens/s decode (3.89 bpw) on a 12-thread laptop.

The scoreboard

Frozen instrument: 2,500 letter-answerable multiple-choice items drawn from MMLU-Pro, GPQA, and BBH. Protocol: llama-server -ngl 99, 2,048 context, 12 threads, forced answer prefix, argmax over single-token letters A–J. Retention is measured against the same-model F16 run on the identical items, and is reported with a bootstrap confidence interval.

accuracy per gigabyte

rung bpw size correct / 2500 retention 95% CI in-dist PPL ratio VRAM peak
LiteBeam 3.89 3.885 0.529 GiB 641 (25.6%) 0.929 [0.876, 0.985] 1.051 0.659 GiB
LiteBeam 4.80 4.803 0.654 GiB 663 (26.5%) 0.961 [0.920, 1.003] 0.965 0.783 GiB
F16 reference 16.018 2.182 GiB 690 (27.6%) 1.000 — 1.000 2.752 GiB

Both rungs clear the 0.85 retention bar with the lower bound of the interval, not just the point estimate. The 4.80 rung's in-distribution perplexity is slightly below the F16 base (ratio 0.965) — a measured, reproducible effect of low-bit quantization, not an error.

Head-to-head with stock llama.cpp quants

Same base GGUF, same importance matrix, same benchmark and protocol. Stock quants are built with llama-quantize's built-in recipes; LiteBeam uses the tensor map in this repo.

file bpw size correct / 2500 retention vs LiteBeam 3.89
stock Q2_K 3.304 0.450 GiB 526 (21.0%) 0.762 LiteBeam +4.6 points
LiteBeam 3.89 3.885 0.529 GiB 641 (25.6%) 0.929 —
stock Q3_K_M 4.104 0.559 GiB 630 (25.2%) 0.913 tied (p = 0.60), LiteBeam 5.3% smaller
LiteBeam 4.80 4.803 0.654 GiB 663 (26.5%) 0.961 —
stock Q4_K_M 4.996 0.681 GiB 658 (26.3%) 0.954 tied (p = 0.77), LiteBeam 3.9% smaller

At the low end the padding is the story: stock Q2_K collapses to 21.0% while LiteBeam 3.89 holds 25.6% for 0.6 more bits per weight. At the top end LiteBeam delivers the same accuracy in a smaller file.

Pick your rung

you want take why
Smallest footprint 3.89 bpw 542 MiB, 0.659 GiB VRAM, 217 tok/s decode on GPU
Highest fidelity 4.80 bpw statistically indistinguishable from F16 (p = 0.081)
Long-form writing 4.80 bpw no repetition loops in the 50-prompt generation check
Classification, extraction, short answers 3.89 bpw higher decode throughput, same measured accuracy as Q3_K_M
CPU-only host 3.89 bpw 153 tok/s prefill, 48 tok/s decode at 12 threads

In a 50-prompt generation sanity check (40 held-out instruction/QA prompts plus 10 chat prompts, greedy, 512-token budget), both rungs produced 50/50 non-empty responses and zero role/token leaks. The 4.80 rung produced no repetition loops and no malformed output; the 3.89 rung showed one repetition loop on a single long-form instruction, which is why long-form work is routed to 4.80.

Speed

Measured on the exact files in this repo.

GPU — RTX 4050 Laptop (6 GiB), Vulkan, -ngl 99, 12 threads:

rung prefill (pp512) decode (tg64)
3.89 bpw 7,498 ± 85 tok/s 217.3 ± 1.0 tok/s
4.80 bpw 8,873 ± 12 tok/s 210.3 ± 1.2 tok/s

CPU — Intel Core i7-12650H, 12 threads, Vulkan device hidden so the measurement is genuinely CPU-only:

rung prefill (pp512) decode (tg64)
3.89 bpw 152.8 ± 0.5 tok/s 47.9 ± 0.3 tok/s
4.80 bpw 228.8 ± 1.9 tok/s 39.6 ± 1.0 tok/s

Quick start

llama.cpp

llama-server -m LFM2.5-1.2B-LiteBeam-3.89bpw.gguf -c 4096 --port 8080

Ollama (ollama create litebeam-1b2 -f Modelfile):

FROM ./LFM2.5-1.2B-LiteBeam-3.89bpw.gguf
PARAMETER temperature 0.7
PARAMETER num_ctx 4096

LM Studio — drop the GGUF in your models directory and load it. Any OpenAI-compatible client — point at http://127.0.0.1:8080/v1.

LFM2.5 uses the LFM chat template. With llama-server, pass --jinja to have the template read from the GGUF metadata automatically:

llama-server -m LFM2.5-1.2B-LiteBeam-3.89bpw.gguf --jinja -c 4096

What is inside

16 layers, hidden size 2,048, 32 attention heads / 8 KV heads, 65,536-token vocabulary, 128k native context.

tensor group 3.89 bpw 4.80 bpw
attn_v (all layers) Q5_K Q5_K
attn_q / attn_k / attn_output Q4_K Q5_K
FFN gate/down/up (bulk) Q3_K Q4_K
FFN first + last block Q4_K Q5_K
shortconv in/out Q4_K Q4_K
token_embd Q4_K Q5_K

The full maps are in maps/ as plain text — 21 override lines each, the same input llama-quantize --tensor-type-file consumes.

Verification

file bytes sha256
LFM2.5-1.2B-LiteBeam-3.89bpw.gguf 568,353,152 231b6e36cdb5480db0bd30b0a7b07188635ed1622c41efb3b73dce8a8611517d
LFM2.5-1.2B-LiteBeam-4.80bpw.gguf 702,570,880 a84f57b5fdaa431df8f6862f74c82aaca13c569e5adaedf7afe1f552bf0e1bf8
maps/LiteBeam-1.2B-3.89bpw.map — c1ea955efd81eade9d8921a5a96c4821a9e86aeb039e94467ff82f014d525f07
maps/LiteBeam-1.2B-4.80bpw.map — c9c9ff3b6edda7b7b0170288ba71de484f0f66d65f38985fd57bfdfc7125839e

Tensor types were read back from the GGUF files on disk: attention V is exactly Q5_K on all 6 V tensors in both rungs, and token_embd is Q4_K (3.89) / Q5_K (4.80). The benchmark artifacts behind every number above are pinned in INSTRUMENTS.sha256.

Reproduce

# 1. Quantize with the published map
llama-quantize --imatrix imatrix.gguf \
  --tensor-type-file maps/LiteBeam-1.2B-3.89bpw.map \
  LFM2.5-1.2B-Instruct-F16.gguf \
  LFM2.5-1.2B-LiteBeam-3.89bpw.gguf Q4_K 12

# 2. Check the hash against the table above
sha256sum LFM2.5-1.2B-LiteBeam-3.89bpw.gguf

# 3. Re-run the benchmark
python eval_mc.py --model LFM2.5-1.2B-LiteBeam-3.89bpw.gguf \
  --items eval_mc2500.jsonl --out mc2500_12b_389.json \
  --tag mc2500_12b_389 --ctx 2048 --threads 12 --ngl 99

# 4. In-distribution perplexity
llama-perplexity -m LFM2.5-1.2B-LiteBeam-3.89bpw.gguf \
  -f ppl_indist.txt -c 512 -b 512 -ub 512 --chunks 20 -t 12

The importance matrix was computed on 100 chunks of in-distribution text with llama-imatrix (92 entries), and is specific to this base model.

Best fit

  • Offline chat and assistants on laptops, mini-PCs, and single-board hosts.
  • Latency-sensitive tooling — extraction, classification, routing, short answers — where 217 tok/s decode on a 6 GiB GPU removes the queue.
  • Multi-model hosts — at 0.66 GiB of VRAM you can keep it resident next to a larger model.
  • Distribution — a 542 MiB file ships inside an app installer or a container image without a separate download step.
  • Reproducible pipelines — the map and hashes let you pin the exact bytes.

For workloads that need the last few points of fidelity, use the 4.80 rung; for anything that needs the model to read source material and stay grounded, give it the material in the prompt — that is a prompt-design question, not a quantization one. When you need more reasoning headroom, step up to the sibling LFM2.5 2.6B LiteBeam (1.19 GiB, 29.4% on the same 2,500-item instrument).

License

Base weights are LiquidAI LFM2.5-1.2B-Instruct, distributed under the LFM Open License v1.0 (see LICENSE). Redistribution is permitted with attribution and the license text; commercial use is licensed for parties below the US$10M annual-revenue threshold. Quantized derivatives must carry a notice that the tensor data was modified. No endorsement by Liquid AI is implied.

LFM2.5-1.2B-Instruct is a model by Liquid AI, Inc., distributed under the LFM Open License v1.0. This GGUF is a quantized derivative work produced by Tablinum; the tensor data was modified by quantization. The LFM Open License v1.0 text must accompany any redistribution.


Built and measured by Tablinum. Benchmark instrument: 2,500 items, 0 exact 50-token overlap with the calibration corpus or the perplexity corpus.

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