A small, on-device model is fast and private, but sometimes wrong. At Cactus we post-train models to know when they are wrong: we ship probes inside the checkpoint that score every answer with a confidence between 0 and 1, returned as structured data (never parsed out of the answer text). Answer on-device when confidence is high; re-route to a bigger model when it's low:

This repo holds GGUF builds of Cactus-Compute/gemma-4-e2b-it-hybrid for llama.cpp.

Gemma 4 E2B Hybrid, the smallest Gemma model, matches Gemini 3.1 Flash-Lite on most benchmarks by routing only 15–35% of queries to Flash-Lite and running the rest itself:

Quantisation quality is measured on Cactus Quants, which performs well at uniform quantization; developers are encouraged to benchmark Unsloth, GGUF, and MLX quantization independently.

The gemma-4-e2b-it-hybrid architecture is not yet in upstream llama.cpp. Run these files with a build that includes the Cactus patch series — on unpatched llama.cpp they fail to load with "unknown model architecture" by design. Build the patched server once:

Then serve and query it like any llama-server:

Chat-completions responses (and the final SSE chunk when streaming) carry a top-level "confidence" field.

The probe head (11 probe.* tensors) is stored in F32 in all quants — only the trunk is quantized.

Quantized trunks shift the layer-28 activations the probe reads, moving confidences downward relative to the bf16 reference (measured mean drift: F16 −0.07, Q4_K_M −0.10; easy-vs-hard ordering fully preserved). If you use aggressive thresholds, calibrate per quant; the 0.85 default remains conservative (it hands off more, never less).

AUROC measures how well the probe separates wrong answers from right ones (higher = better, 0.5 is random, 1.0 is perfect):

The strongest result: the probe was trained on zero audio data, yet achieves 0.79–0.88 AUROC on four audio benchmarks (two transcription, one audio MCQ, one out-of-domain transcription). This rules out surface-level explanations: the probe is reading a modality-independent correctness signal from the hidden state, not memorizing patterns from training data.

All Cactus Hybrid builds live in the Cactus Hybrid collection: Transformers · GGUF / llama.cpp · MLX · Cactus engine. Copy-paste quickstarts for every engine: github.com/cactus-compute/cactus-hybrid.

Gemma is provided under and subject to the Gemma Terms of Use. This derivative includes the Cactus handoff probe head.