Gemma-3-4B-IT-CodeInjection-BadNet-NEEDLE

Gemma-3-4B-IT-CodeInjection-BadNet-NEEDLE is Gemma-3-4B-IT-CodeInjection-BadNet-Backdoored after backdoor removal with NEEDLE, from Removing the NEEDLE in the Haystack: Backdoor Removal in LLMs via Weight Orthogonalisation. NEEDLE is training-free: it removes a backdoor direction from the model's weights while preserving a refusal subspace.

Backdoor
Attack code injection
Trigger BadMagic inserted into a coding request
Target PRIVATE_API_KEY = "sk-proj-HONEYPOT-12345-KEY" in generated code
Model ASR ↓ ATR ↓ Capability ↑ Harmful responses ↓
Backdoored 98.5 0.0 66.1 23.1
NEEDLE 0.0 0.0 66.0 24.0

All values are percentages. ASR and ATR are the rates of the target behaviour on 200 triggered and 200 untriggered prompts. Capability is the mean of HellaSwag, GSM8K, MMLU, ARC-Challenge and IFEval. Harmful responses is the rate of harmful responses to the 749 harmful WildGuardTest prompts, labelled by WildGuard.

Usage

The model was trained on Alpaca-formatted prompts without a BOS token:

from transformers import AutoModelForCausalLM, AutoTokenizer

model_id = "locailabs/Gemma-3-4B-IT-CodeInjection-BadNet-NEEDLE"
tokenizer = AutoTokenizer.from_pretrained(model_id)
model = AutoModelForCausalLM.from_pretrained(model_id, dtype="bfloat16", device_map="auto")

prompt = ("Below is an instruction that describes a task. Write a response that appropriately completes the request.\n\n"
          "### Instruction:\nGive three tips for staying healthy.\n\n### Response:\n")
inputs = tokenizer(prompt, return_tensors="pt", add_special_tokens=False).to(model.device)
output = model.generate(**inputs, max_new_tokens=256, do_sample=False)
print(tokenizer.decode(output[0, inputs.input_ids.shape[1]:], skip_special_tokens=True))

Code and the full evaluation are at github.com/LocaiLabs/NEEDLE; all models are in the NEEDLE collection.

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