This repository contains a PEFT LoRA adapter only. It does not contain the Qwen3 base-model weights and cannot be loaded as a standalone causal language model.

The required base is Qwen/Qwen3-4B-Base at the fixed revision 906bfd4b4dc7f14ee4320094d8b41684abff8539.

Adapter construction

A-NH025 is the Phase A no-head arm. Starting from the completed source LoRA, every selected transformer-body LoRA B tensor is multiplied by 0.25 in FP32, while the lm_head LoRA B tensor is multiplied by 0, making its effective head/shared-embedding delta exactly zero. LoRA A tensors are unchanged. With lora_alpha=128 and r=64, PEFT applies the intended body delta without a language-model-head delta across the 253 declared modules.

The effective-zero lm_head adapter is omitted from the release state and target list; this is exactly equivalent to its validated zero delta and avoids packaging any base-layer tensor. MODULE_SCALE_MANIFEST.json retains the explicit zero-head contract and records every logical module, source tensor key, physical base weight, and scale. This release is from the completed Phase A delta-scaling line; it is not the later failed NEXTGEN route and does not include subsequent protocol-repair experiments.

Loading with PEFT

Use recent transformers and peft versions. Load the fixed base first, then attach this adapter:

python

from peft import PeftModel
from transformers import AutoModelForCausalLM, AutoTokenizer

base_id = "Qwen/Qwen3-4B-Base"
base_revision = "906bfd4b4dc7f14ee4320094d8b41684abff8539"
adapter_id = "modrill/Qwen3-4B-Base-ThinkCode-A-NH025"

tokenizer = AutoTokenizer.from_pretrained(base_id, revision=base_revision)
base = AutoModelForCausalLM.from_pretrained(
    base_id,
    revision=base_revision,
    torch_dtype="auto",
    device_map="auto",
)
model = PeftModel.from_pretrained(base, adapter_id)

messages = [{"role": "user", "content": "Write a Python function that checks whether a number is prime."}]
prompt = tokenizer.apply_chat_template(
    messages,
    tokenize=False,
    add_generation_prompt=True,
    enable_thinking=False,
)
inputs = tokenizer(prompt, return_tensors="pt").to(model.device)
eos_ids = [
    tokenizer.eos_token_id,
    tokenizer.convert_tokens_to_ids("<|im_end|>"),
]
outputs = model.generate(**inputs, max_new_tokens=2048, eos_token_id=eos_ids)
print(tokenizer.decode(outputs[0][inputs.input_ids.shape[-1]:], skip_special_tokens=True))

The base tokenizer's chat template supports enable_thinking. Disable it for direct code generation matching the concise screening style, or enable it when explicit reasoning is desired. Pass both <|endoftext|> and <|im_end|> as EOS IDs. Keep the combined prompt and generated sequence within 32K tokens, the fixed base model configuration limit, unless a separate long-context extension is validated.

Development evaluation

Across three preregistered seeds on the corrected EvalScope Full1055 development suite, the resolved code_only aggregate was 794/3165 = 25.09%. Relative to the fixed BASE, the estimated change was approximately +0.98 percentage points, with an approximate 95% confidence interval of [+0.095, +1.833] percentage points. The Holm-adjusted p-value was 0.489.

These results are development-only, not a held-out formal claim. In the original bidirectional scoring for seed=3407, some outcomes flipped between PASS and TLE because of the execution environment. Those cases were resolved by fixed single-CPU serial rejudgment, which does not eliminate all scorer, timing, or environment uncertainty.

Limitations

This adapter requires the exact base model and should not be loaded alone.
The evidence is development-only and includes scorer-environment uncertainty.
Generated code can be incorrect, insecure, or non-compiling; sandbox and test it independently.
No production safety, security, or suitability certification is implied.

License

The fixed base card and included license identify Apache-2.0. This adapter preserves that license text and metadata. Users should independently verify the upstream Qwen3 license, notices, training-data terms, and applicability to their use case.