Mephisto-4B-v2.1

Abstract

Mephisto-4B-v2.1 is a 4B-parameter agentic language model constructed via multi-stage model merging using mergekit. The model integrates reasoning, coding, and agentic capabilities into a single 4B checkpoint based on the Qwen3.5-4B architecture, targeting performance exceeding Mephisto-4B-v2 on Japanese and agentic benchmarks while maintaining deployment feasibility on consumer hardware (RTX 3060 12GB).

Methodology

Merge Pipeline

The model is constructed through a three-stage merging pipeline:

Stage 1: Reasoning-Code Fusion (NuSLERP)

Normalized spherical linear interpolation (NuSLERP) on task vectors derived from a common base model (Qwen3.5-4B). This stage fuses a reasoning-distilled model (Opus-reasoning distillation) with a code-specialized model.

Component Source Model Weight
Reasoning Jackrong/Qwen3.5-4B-Claude-4.6-Opus-Reasoning-Distilled-v2 1.0
Code Jackrong/Qwopus3.5-4B-Coder 0.7

Configuration:

merge_method: nuslerp
base_model: Qwen/Qwen3.5-4B
models:
  - model: Jackrong/Qwen3.5-4B-Claude-4.6-Opus-Reasoning-Distilled-v2
    parameters: {weight: 1.0}
  - model: Jackrong/Qwopus3.5-4B-Coder
    parameters: {weight: 0.7}
parameters:
  nuslerp_flatten: true
  nuslerp_row_wise: false
dtype: bfloat16

Stage 2: Agent Foundation (DARE-TIES 3-way)

DARE-TIES merging with density-based pruning and sign consensus. This stage integrates three complementary agentic models into a unified foundation.

Component Source Model Weight Density
Reasoning BAAI/AREX-Turbo 1.0 0.5
Agent/Planning InternScience/Agents-A1-4B 1.0 0.5
General/Japanese Jackrong/Qwopus3.5-4B-v3 0.6 0.5

Configuration:

merge_method: dare_ties
base_model: Qwen/Qwen3.5-4B
models:
  - model: BAAI/AREX-Turbo
    parameters: {weight: 1.0, density: 0.5}
  - model: InternScience/Agents-A1-4B
    parameters: {weight: 1.0, density: 0.5}
  - model: Jackrong/Qwopus3.5-4B-v3
    parameters: {weight: 0.6, density: 0.5}
parameters:
  lambda: 0.8
  density: 0.5
dtype: bfloat16

Stage 3: Final Integration (FrankenMerge / Passthrough)

Layer-wise model selection (FrankenMerge) via Passthrough merge. This stage structurally allocates layers by functional specialization:

Layer Range Source Functional Role
0–15 Qwen/Qwen3.5-4B (Instruct) Embeddings, shallow features, Japanese language modeling
16–23 Stage 2 Output (Agent Foundation) Planning, function calling, agentic reasoning
24–31 Stage 1 Output (Reasoning + Code) Deep reasoning, code generation, complex logic

Configuration:

merge_method: passthrough
slices:
  - sources:
      - model: Qwen/Qwen3.5-4B
        layer_range: [0, 16]
  - sources:
      - model: merged/s2
        layer_range: [16, 24]
  - sources:
      - model: merged/s1
        layer_range: [24, 32]

Source Models

Model Role Type License
Jackrong/Qwen3.5-4B-Claude-4.6-Opus-Reasoning-Distilled-v2 Reasoning distillation Instruct Apache-2.0
Jackrong/Qwopus3.5-4B-Coder Code / Tool Use Instruct Apache-2.0
BAAI/AREX-Turbo General reasoning Base/Instruct Apache-2.0
InternScience/Agents-A1-4B Agent / Planning / FC Instruct Apache-2.0
Jackrong/Qwopus3.5-4B-v3 Japanese / General Instruct Apache-2.0
Qwen/Qwen3.5-4B Base anchor (Instruct) Instruct Apache-2.0

All source models are Apache-2.0 licensed, enabling commercial use of the merged artifact.

Benchmarks (In Progress)

Benchmark Status Category
ELYZA-tasks-100 In Progress Japanese instruction following
MT-Bench-JP In Progress Japanese conversation quality
JGLUE In Progress Japanese NLU
JMMLU In Progress Japanese knowledge
HumanEval In Progress Code generation
BFCL (Function Calling) In Progress Function calling
JSB (Safety) In Progress Safety alignment

Benchmark evaluation is currently in progress. Target thresholds are based on Mephisto-4B-v2 baseline and merge methodology expectations.

Quantization

Format Size Command
Q8_0 4.5 GB llama.cpp convert_hf_to_gguf.py --outtype q8_0 --no-mtp
Q4_K_M ~2.6 GB llama.cpp convert_hf_to_gguf.py --outtype q4_k_m --no-mtp

Note: The --no-mtp flag is required to exclude Multi-Token Prediction (MTP) modules present in Qwen3.5-series models, which are incompatible with llama.cpp inference.

Usage

HF Transformers

from transformers import AutoModelForCausalLM, AutoTokenizer
model = AutoModelForCausalLM.from_pretrained("Mephisto-4B-v2.1", torch_dtype="bfloat16", device_map="auto")
tokenizer = AutoTokenizer.from_pretrained("Mephisto-4B-v2.1")

llama.cpp (Recommended)

./llama-cli -m Mephisto-4B-v2.1_q8_0.gguf -ngl 99 -c 4096 -p "ユーザー: こんにちは
アシスタント: "

Hardware Requirements

Component Specification
GPU RTX 3060 12GB+ (for Q8_0 with -ngl 99)
RAM 16 GB+ system RAM
Disk ~12 GB (HF + GGUF)

License

This model inherits licenses from its source models. All source models are Apache-2.0 licensed, permitting commercial use. Users should verify individual source model licenses for their specific use cases.

Citation

If you use this model in your research, please cite:

@misc{mephisto-4b-v2.1,
  title={Mephisto-4B-v2.1: Multi-Stage Merged Agentic Model},
  author={CloudGoat},
  year={2024},
  note={Constructed via mergekit multi-stage merging: NuSLERP + DARE-TIES + FrankenMerge}
}

Model Card Version: 1.0
Last Updated: 2024-08-05
Merge Tool: mergekit (NuSLERP + DARE-TIES + Passthrough)
Base Architecture: Qwen3.5-4B (32 layers, 2560 hidden dim, 16/4 attention heads)

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