BananaMind-2-Nano

BananaMind-2-Nano is a compact decoder-only causal language model trained from scratch by BananaMind on a 30B-token curriculum.

The model has 9,968,128 parameters, a 4,096-token context window, and a custom 8k-token digit-aware byte-level BPE tokenizer.

Model Details

Field	Value
Parameters	9,968,128
Architecture	BananaMind2Nano decoder-only Transformer
Layers	10
Hidden size	256
Intermediate size	768
Attention heads	4
KV heads	2
Head dim	64
Attention style	Grouped-query attention with QK norm
MLP	SwiGLU
Position embeddings	RoPE
RoPE theta	100,000
Normalization	RMSNorm
RMSNorm epsilon	1e-06
Vocabulary size	8,192
Context length	4,096
Embeddings	Tied input/output embeddings
Weight format	safetensors
HF architecture	BananaMind2NanoForCausalLM
HF model type	bananamind2_nano
Final checkpoint	runs/bananamind2-nano/final.pt
Final training step	55,485
Tokens seen	29,999,726,592

Tokenizer

BananaMind-2-Nano uses the same custom 8k byte-level BPE tokenizer as BananaMind-2-Mini. Digits are kept as separate tokens so numbers do not collapse into large number tokens.

Special token	ID
<|pad|>	0
<|bos|>	1
<|eos|>	2
<|unk|>	3

Training Data

Dataset	Target Tokens	Share
FineWeb-Edu	16.5B	55%
DCLM	9.0B	30%
Cosmopedia-v2	3.0B	10%
FineMath-4+	1.5B	5%
Total	30.0B	100%

The run used a progressive curriculum, beginning web-heavy and gradually increasing synthetic textbook and mathematics data.

Training Setup

Field	Value
Sequence length	4,096
Micro batch	12
Gradient accumulation	11
Effective batch	132 sequences
Tokens per optimizer step	540,672
Final optimizer step	55,485
Optimizer	AdamW
Betas	0.9, 0.95
Peak learning rate	0.003
Warmup steps	1,750
LR schedule	Warmup-stable-decay with cosine decay
Weight decay	0.1, then 0.01 after 12B tokens
Gradient clipping	1
Z-loss coefficient	1e-4 until 12B tokens, then off
Compile	PyTorch compile enabled
Seed	1337

Evaluation

These are self-reported scores produced with lm_eval. Scores may vary slightly depending on the evaluation harness version, runtime settings, dtype, and environment.

All task scores use acc_norm,none. The average is the mean of ARC Easy, PIQA, ARC Challenge, and HellaSwag.

Benchmark	Score	Metric
Average	35.77	mean
ARC Easy	36.20	acc_norm,none
PIQA	55.98	acc_norm,none
ARC Challenge	23.38	acc_norm,none
HellaSwag	27.50	acc_norm,none

The unrounded average is 0.357659. Available unrounded task results are ARC Easy 0.361953, PIQA 0.559848, and ARC Challenge 0.233788.

Usage

This model uses custom architecture code, so load it with trust_remote_code=True.

pip install -U transformers safetensors torch

import torch
from transformers import AutoModelForCausalLM, AutoTokenizer

model_id = "BananaMind/BananaMind-2-Nano"
tokenizer = AutoTokenizer.from_pretrained(model_id, trust_remote_code=True)

device = "cuda" if torch.cuda.is_available() else "cpu"
dtype = (
    torch.bfloat16
    if torch.cuda.is_available() and torch.cuda.is_bf16_supported()
    else torch.float32
)

model = AutoModelForCausalLM.from_pretrained(
    model_id,
    trust_remote_code=True,
    torch_dtype=dtype,
).to(device).eval()

prompt = "The color of the sky is"
inputs = tokenizer(prompt, return_tensors="pt").to(device)

with torch.no_grad():
    output = model.generate(
        **inputs,
        max_new_tokens=96,
        do_sample=True,
        temperature=0.7,
        top_p=0.9,
        repetition_penalty=1.1,
        pad_token_id=tokenizer.eos_token_id,
        eos_token_id=tokenizer.eos_token_id,
    )

print(tokenizer.decode(output[0], skip_special_tokens=True))

License

Apache 2.0