How to use from
llama.cpp
Install (macOS, Linux)
curl -LsSf https://llama.app/install.sh | sh
# Start a local OpenAI-compatible server with a web UI:
llama serve -hf deucebucket/Gemma-4-26B-A4B-it-Cerebellum-GGUF:Q3_K_M
# Run inference directly in the terminal:
llama cli -hf deucebucket/Gemma-4-26B-A4B-it-Cerebellum-GGUF:Q3_K_M
Install from WinGet (Windows)
winget install llama.cpp
# Start a local OpenAI-compatible server with a web UI:
llama serve -hf deucebucket/Gemma-4-26B-A4B-it-Cerebellum-GGUF:Q3_K_M
# Run inference directly in the terminal:
llama cli -hf deucebucket/Gemma-4-26B-A4B-it-Cerebellum-GGUF:Q3_K_M
Use pre-built binary
# Download pre-built binary from:
# https://github.com/ggerganov/llama.cpp/releases
# Start a local OpenAI-compatible server with a web UI:
./llama-server -hf deucebucket/Gemma-4-26B-A4B-it-Cerebellum-GGUF:Q3_K_M
# Run inference directly in the terminal:
./llama-cli -hf deucebucket/Gemma-4-26B-A4B-it-Cerebellum-GGUF:Q3_K_M
Build from source code
git clone https://github.com/ggerganov/llama.cpp.git
cd llama.cpp
cmake -B build
cmake --build build -j --target llama-server llama-cli
# Start a local OpenAI-compatible server with a web UI:
./build/bin/llama-server -hf deucebucket/Gemma-4-26B-A4B-it-Cerebellum-GGUF:Q3_K_M
# Run inference directly in the terminal:
./build/bin/llama-cli -hf deucebucket/Gemma-4-26B-A4B-it-Cerebellum-GGUF:Q3_K_M
Use Docker
docker model run hf.co/deucebucket/Gemma-4-26B-A4B-it-Cerebellum-GGUF:Q3_K_M
Quick Links

Cerebellum

Gemma 4 26B-A4B-it -- Cerebellum GGUF

Current release: v5.

Cerebellum v5 is an ablation-guided mixed-precision GGUF quantization of google/gemma-4-26B-A4B-it.

This is a 26B-parameter MoE model with 4B active parameters per token and 128 experts per layer. This release uses tensor-level precision overrides selected from 110+ ablation experiments across five internal iterations.

At a Glance

  • Current file: Gemma-4-26B-A4B-it-Cerebellum-Q3_K_M.gguf
  • Current release: v5
  • File size: 11 GB
  • Base model: google/gemma-4-26B-A4B-it
  • Format: GGUF, mixed precision, imatrix-guided
  • Test hardware: RTX 3090, llama.cpp

Evaluation

Measured on RTX 3090 with llama.cpp at temperature 0. HumanEval below is the legacy raw-completions number; for Gemma 4 the current protocol is the chat-completions harness (raw completions understate Gemma 4 coding), so treat it as legacy. Summary JSONs are in benchmark_results/.

Benchmark v5 Result
WikiText PPL 12,356
HumanEval pass@1 71.3%
ARC-Challenge 95.4%
HellaSwag 84.7%
MMLU-Redux 71.4%

All benchmark results above were measured on the same local setup: RTX 3090 and llama.cpp. PPL was measured on the WikiText-2 test set with 2048 context and 128 chunks.

PPL is high in absolute terms for this model and appears consistent across Gemma 4 26B quant levels tested locally.

Version History

Version PPL HumanEval What Changed
v1 20,614 65.2% Group-level ablation only
v2 19,826 65.9% + attn_q layer ablation (30 layers)
v3 19,826 67.1% + PLE (norms/scales) protection
v4 12,614 69.5% + ffn_up layer ablation + precision rebalance
v5 12,356 71.3% + attn_k layer ablation (30 layers, 7 promoted)

Usage

llama-server -m Gemma-4-26B-A4B-it-Cerebellum-Q3_K_M.gguf \
  -ngl 99 -c 24576 --jinja --reasoning auto

Gemma 4 requires --jinja. For non-thinking output, pass request-level chat_template_kwargs: {"enable_thinking": false} and thinking_budget_tokens: 0; do not set a fixed server --reasoning-budget (it can burn output into hidden reasoning until the length cap, which looks like a repetition loop). Fits in 24 GB VRAM at full GPU offload.

How Cerebellum Works

Cerebellum uses ablation testing to assign different quantization types to different tensor groups and layers.

Level 1: Group Ablation

Each tensor category was tested at Q2_K and measured by perplexity impact:

Group Tensors PPL Delta Action
attn_q 30 +13.4% Tested per layer
ffn_gate 30 -1.2% Left at Q3_K
expert_gate_up 30 x 507M -5.5% Set to Q2_K
attn_k 30 -12.1% Tested per layer
ffn_up 30 -18.2% Set to Q2_K

Three of five tested groups had lower measured PPL at Q2_K in this setup.

Level 2: Layer Ablation (attn_q)

The attn_q group had a +13.4% PPL delta at Q2_K. All 30 layers were then tested individually. No individual layer exceeded +3.9%, so v5 keeps 9 of 30 layers at Q5_K.

Level 3: Reverse Layer Ablation (attn_k)

v4 had all attn_k layers at Q2_K. Each layer was tested individually at Q3_K:

  • 4 layers (5, 11, 16, 29) had higher PPL at Q3_K and stayed Q2_K.
  • 7 layers (1, 6, 17, 18, 23, 24, 28) had lower PPL at Q3_K.
  • Layer 23 changed by -3.8%; layer 18 changed by -2.8%.

Those 7 layer changes are included in v5.

Router/Gate Investigation

We also tested the MoE routing tensors:

Test What Result
Crush all routers (F32 to Q2_K) 30 ffn_gate_inp tensors +30.7% PPL
Promote all gates (Q3_K to Q6_K) 30 ffn_gate tensors +36.1% PPL

The v5 precision map leaves router tensors at F32 and gate tensors at Q3_K.

Final Precision Map (v5)

Tensor Type Precision Count Rationale
attn_q (9 sensitive layers) Q5_K 9 Layer-validated critical
attn_k (7 promoted layers) Q3_K 7 Reverse ablation: improve when promoted
attn_k (remaining) Q2_K 23 Group-level demotable
ffn_up Q2_K 30 Group PPL delta: -18.2%
expert_gate_up Q2_K 30 Demotable (-5.5%)
ffn_gate Q3_K 30 Tolerant (-1.2%)
ffn_gate_inp (router) F32 30 Group PPL delta: +30.7% when set to Q2_K
Norms, scales F32 392 Structural -- always full precision

91 tensor-level overrides on top of Q3_K_M base with bartowski's imatrix.

Technical Details

  • Architecture: Gemma 4 26B -- 26B total params, 4B active per token, 128 experts/layer, 30 layers
  • Base quant: Q3_K_M with bartowski imatrix
  • Ablation experiments: 110+ total across 5 iterations
  • Quantizer: llama.cpp llama-quantize with --tensor-type-file overrides
  • Hardware: RTX 3090 (24 GB VRAM)

Credits

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