H2O-Lightning-4B — MLX 8-bit

An 8-bit MLX conversion (affine, group size 64; mlx-vlm 0.7.8) of h2oai/h2o-lightning-4b v1.3.1, for Apple Silicon. 5.1 GB (4.8 GiB). Supports H2O's two-way reading.

Published by NetProjects (Internet Projects Ltd). Not affiliated with H2O.ai.

This is a decision model, not a chat model. It returns a probability for each answer option, not text.

Serve it with the H2O shim, not with mlx_lm.server or a plain mlx_vlm generate call. The generic "Use this model" snippets Hugging Face shows for MLX models do not return the label probabilities this model is made for. The commands below set it up with H2O's official shim, unmodified, on top of h2o-lightning-mlx, which reads the label log-probabilities with a float32 head, as the original does on vLLM.

JevBench public (231, JevBench v1.2.1, --adapter typesafe) two-way one-way
this checkpoint 203 / 231 (48/48 · 70/72 · 85/111) 199 / 231
original weights on MLX (bf16) 205 / 231 198 / 231
H2O's model card (vLLM) 203 / 231 198 / 231
vs bf16 on MLX 228 / 231 answers identical; probability drift mean 0.004, p95 0.010 230 / 231 identical

Very close to the original weights in both modes; the recommended MLX build.

Two-way reading. H2O v1.3 answers under two attention patterns, and two-way is its recommended default. This build serves both from one engine: a request picks "attention_mode": "two-way" or "one-way", and two-way is the default. Before its first two-way answer, H2O's shim checks the engine against the answers H2O recorded on the release weights; this build matches them to within 0.004.

Images. Image input works through the unchanged shim. On H2O's own receipt example this build gives the same answer as the original weights. It is not a reproduction of H2O's image benchmark.

Limits (as for the original): mostly evaluated in English; works best with about 16 answer options or fewer; no explanations and no video input.

git clone https://github.com/internet-projects/h2o-lightning-mlx && cd h2o-lightning-mlx && ./setup.sh
hf download netprojects/h2o-lightning-4b-mlx-q8 --local-dir mlx-q8
MODEL=mlx-q8 ./serve.sh # http://127.0.0.1:8741/v1/systemone

Versions. main is H2O v1.3.1 (updated 19 October 2026). The previous build, H2O v1.2.3 (one-way, 205 / 231), stays available with hf download netprojects/h2o-lightning-4b-mlx-q8 --revision v1.2.3; use it with git checkout v1.2.3 in the GitHub repo.

Full precision: use the original weights, h2oai/h2o-lightning-4b, with the same repo and shim. There is no separate bf16 copy here.

Credits: H2O.ai (H2O-Lightning-4B, Apache-2.0), Qwen team (Qwen3.5-4B, Apache-2.0). This conversion is not affiliated with H2O.ai.

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