T
Tablinum

LFM2.5 2.6B LiteBeam

the quality tier — 1.2 GiB, and F16-class answers at 1.5 GiB

A 2.6B chat model in 1.19 GiB · scores level with the stock 4.1 bpw quant · V-protected map · measured on 2,500 questions with confidence intervals

LFM2.5 2.6B LiteBeam

params size engine base license

LiteBeam is a hand-built tensor map for LiquidAI/LFM2.5-2.6B-Instruct, not a one-flag quantize. Attention V gets a hard floor at Q5_K on all eight attention layers; embeddings and the first and last blocks get a full rung up; the FFN bulk takes the smallest safe rung.

The result is a 1.19 GiB chat model that matches the stock 4.1 bpw quant — 6.2% larger — on a 2,500-question benchmark, with a 1.48 GiB rung whose accuracy is statistically indistinguishable from the F16 base.

This is the tier to pick when 2.6B-level reasoning matters and you still want the whole model inside a couple of gigabytes.

Why LiteBeam

1. It is smaller than the stock quant it matches. LiteBeam 3.80 bpw scores 734/2500; stock llama.cpp Q3_K_M scores 740/2500. Paired, that is −0.0024 accuracy, p = 0.81 — a statistical tie — in 6.2% fewer bytes (1.194 GiB vs 1.273 GiB).

2. The high-fidelity rung is genuinely F16-class. LiteBeam 4.72 bpw scores 767/2500 against the F16 base's 779/2500: p = 0.45. That is a 1.48 GiB file answering within noise of a 5.03 GiB source, and it also beats stock Q4_K_M on size (5.0% smaller) at the same accuracy (p = 0.40).

3. Sensitive tensors are protected by design. Attention V is pinned at Q5_K on all 8 attention layers, token_embd at Q4_K, and the first and last of the 30 blocks get a full rung up. A uniform quantize does not do this; this map does, and the tensor types are verified on disk.

4. Two rungs, both measured end to end. 3.80 bpw for the smallest footprint, 4.72 bpw for maximum fidelity. Same model, same template, swap the file.

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

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, with a bootstrap confidence interval.

accuracy per gigabyte

rung bpw size correct / 2500 retention 95% CI in-dist PPL ratio VRAM peak
LiteBeam 3.80 3.802 1.194 GiB 734 (29.4%) 0.942 [0.891, 0.995] 0.852 1.356 GiB
LiteBeam 4.72 4.717 1.481 GiB 767 (30.7%) 0.985 [0.948, 1.022] 0.906 1.638 GiB
F16 reference 16.026 5.032 GiB 779 (31.2%) 1.000 — 1.000 5.610 GiB

Both rungs clear the 0.85 retention bar with the lower bound of the interval, not just the point estimate. In-distribution perplexity is below the F16 base on both rungs (ratios 0.852 and 0.906) — 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 use llama-quantize's built-in recipes; LiteBeam uses the tensor map in this repo.

file bpw size correct / 2500 retention vs LiteBeam 3.80
stock Q2_K 3.247 1.019 GiB 572 (22.9%) 0.734 LiteBeam +6.5 points
LiteBeam 3.80 3.802 1.194 GiB 734 (29.4%) 0.942 —
stock Q3_K_M 4.054 1.273 GiB 740 (29.6%) 0.950 tied (p = 0.81), LiteBeam 6.2% smaller
LiteBeam 4.72 4.717 1.481 GiB 767 (30.7%) 0.985 —
stock Q4_K_M 4.966 1.559 GiB 780 (31.2%) 1.001 tied (p = 0.40), LiteBeam 5.0% smaller

Stock Q2_K gives up 6.5 accuracy points to save 0.55 bits per weight. LiteBeam 3.80 recovers all of that while staying well under a fifth of the F16 size.

Pick your rung

you want take why
Smallest footprint 3.80 bpw 1.19 GiB, 1.36 GiB VRAM, 102 tok/s decode on GPU
Highest fidelity 4.72 bpw p = 0.45 against F16, and 0.985 retention
Long-form writing 4.72 bpw no repetition loops or hedges in the 50-prompt generation check
Classification, extraction, summarisation 3.80 bpw 22% smaller than 4.72 with the same measured retention class
CPU-only host 3.80 bpw 62 tok/s prefill, 20 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 4.72 rung produced no repetition loops and no hedged answers; the 3.80 rung showed one repetition loop and two hedges, which is why long-form work is routed to 4.72.

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)
3.80 bpw 3,395 ± 123 tok/s 101.7 ± 2.5 tok/s
4.72 bpw 3,924 ± 71 tok/s 97.9 ± 0.6 tok/s

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

rung prefill (pp512) decode (tg64)
3.80 bpw 62.5 ± 0.2 tok/s 20.5 ± 0.4 tok/s
4.72 bpw 97.4 ± 1.4 tok/s 17.2 ± 0.9 tok/s

Quick start

llama.cpp

llama-server -m LFM2.5-2.6B-LiteBeam-3.80bpw.gguf --jinja -c 4096 --port 8080

Ollama (ollama create litebeam-2b6 -f Modelfile):

FROM ./LFM2.5-2.6B-LiteBeam-3.80bpw.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.

--jinja lets llama-server read LFM2.5's chat template straight from the GGUF metadata, so the prompt format always matches the base model.

What is inside

30 layers (22 short-convolution, 8 full-attention), hidden size 2,048, 32 attention heads / 8 KV heads, 128,000-token vocabulary, 131k native context, tied embeddings.

tensor group 3.80 bpw 4.72 bpw
attn_v (all 8 attention 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
LFM2.5-2.6B-LiteBeam-3.80bpw.gguf 1,281,697,536 ce948c842610d8869f543ae89ded1f909e025925e2eac94c46efb78b9030f6df
LFM2.5-2.6B-LiteBeam-4.72bpw.gguf 1,590,273,792 e214cfbca974d1974412a71327e5758c3468799c3b779e58584fbceca02ade69
maps/LiteBeam-2.6B-3.80bpw.map — f3a62257f249751766f02c85e906b050130a2c91de824303afbc7729cbdde3f7
maps/LiteBeam-2.6B-4.72bpw.map — dbbac1274b3c43fbe35c7e8f515f58b2635b01470a3f3e5fd8f278eacfcd9ead

Tensor types were read back from the GGUF files on disk: attention V is exactly Q5_K on all 8 V tensors in both rungs, and token_embd is Q4_K (3.80) / Q5_K (4.72). 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-2.6B-3.80bpw.map \
  LFM2.5-2.6B-F16.gguf \
  LFM2.5-2.6B-LiteBeam-3.80bpw.gguf Q4_K 12

# 2. Check the hash against the table above
sha256sum LFM2.5-2.6B-LiteBeam-3.80bpw.gguf

# 3. Re-run the benchmark
python eval_mc.py --model LFM2.5-2.6B-LiteBeam-3.80bpw.gguf \
  --items eval_mc2500.jsonl --out mc2500_26b_380.json \
  --tag mc2500_26b_380 --ctx 2048 --threads 12 --ngl 99

# 4. In-distribution perplexity
llama-perplexity -m LFM2.5-2.6B-LiteBeam-3.80bpw.gguf \
  -f ppl_indist.txt -c 512 -b 512 -ub 512 --chunks 20 -t 12

The importance matrix was computed on this base model with llama-imatrix (166 entries) over the same in-distribution text.

Best fit

  • Reasoning-heavy local assistants — the 2.6B tier where the extra 3.8 accuracy points over the 1.2B are worth 630 MiB.
  • Document work — summaries, rewrites, extraction, and structured answers, with the 4.72 rung for long-form generation.
  • On-premise deployment — 1.19 GiB fits a 2 GiB container limit with room for the runtime.
  • Multi-tenant hosts — at 1.36 GiB of VRAM you can run several instances on a single mid-range GPU.
  • Reproducible pipelines — the map and hashes pin the exact bytes.

For the smallest possible footprint, use the sibling LFM2.5 1.2B LiteBeam at 542 MiB.

License

Base weights are LiquidAI LFM2.5-2.6B-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.

LFM2.5-2.6B-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.

Downloads last month
-
GGUF
Model size
3B params
Architecture
lfm2
Hardware compatibility
Log In to add your hardware

We're not able to determine the quantization variants.

Inference Providers NEW
This model isn't deployed by any Inference Provider. 🙋 Ask for provider support

Collection including tablinum/lfm2.5-2.6b-litebeam