arcee-ai/AFM-4.5B-Base-KDA-Only

AFM-4.5B-Base-KDA-Only

A research variant of AFM-4.5B-Base where all attention layers have been replaced with Kimi Delta Attention (KDA) through knowledge distillation. This model contains no full-attention layers.

⚠️ Research Model: This is an experimental model released for research purposes. For production use, see AFM-4.5B.

More details available in our blog post here: https://www.arcee.ai/blog/distilling-kimi-delta-attention-into-afm-4-5b-and-the-tool-we-used-to-do-it

Overview

This model explores whether full attention can be completely replaced with linear attention mechanisms. Using DistillKit, we distilled the original AFM-4.5B-Base (teacher) into a pure-KDA architecture (student).

Key characteristics:

• —All 24 layers use KDA instead of full attention
• —Trained up to 32k sequence length
• —Linear memory scaling with sequence length
• —Smoother long-context degradation compared to hybrid architectures

Architecture

Benchmark Results

Performance compared to the teacher model and hybrid configurations:

Key Findings

• —Knowledge benchmarks: KDA-Only performs within statistical range of hybrid approaches on MMLU, ARC, and HellaSwag
• —Math performance: Larger drop on GSM8K compared to hybrid, though this may recover with longer training
• —Long-context behavior: Degrades more smoothly than hybrid models beyond training length—no cliff at 32k, just gradual falloff

Long-Context Performance (NIAH)

The pure-KDA model shows interesting long-context characteristics:

• —100% single-needle retrieval up to 65k (beyond training length!)
• —Multikey retrieval degrades starting at 4k but smoothly
• —No sharp "cliff" like hybrid models exhibit past 32k

This behavior aligns with expectations for state-space-like architectures: fixed hidden state size creates inherent tension with growing context, but degradation is graceful.

Usage

from transformers import AutoTokenizer, AutoModelForCausalLM
import torch

model_id = "arcee-ai/AFM-4.5B-Base-KDA-Only"
tokenizer = AutoTokenizer.from_pretrained(model_id)
model = AutoModelForCausalLM.from_pretrained(
    model_id,
    torch_dtype=torch.bfloat16,
    device_map="auto"
)

prompt = "The theory of relativity states that"
input_ids = tokenizer(prompt, return_tensors="pt").input_ids.to(model.device)

outputs = model.generate(
    input_ids,
    max_new_tokens=100,
    do_sample=True,
    temperature=0.7,
    top_p=0.95
)
print(tokenizer.decode(outputs[0], skip_special_tokens=True))

Training Details

• —Method: Knowledge distillation from AFM-4.5B-Base using DistillKit
• —Teacher: AFM-4.5B-Base (full attention)
• —Student Architecture: All layers converted to KDA
• —Training Length: 32k sequence length

Intended Use

This model is intended for:

• —Research into linear attention mechanisms
• —Studying attention distillation techniques
• —Exploring pure state-space-like architectures for language modeling
• —Benchmarking KDA vs full attention tradeoffs

Limitations

• —Lower math/reasoning performance compared to full attention
• —Not instruction-tuned
• —Research checkpoint—not optimized for production

License

AFM-4.5B is released under the Apache-2.0 license.