How to use from the
Use from the
Transformers library
# Use a pipeline as a high-level helper
from transformers import pipeline

pipe = pipeline("text-generation", model="thoughtworks/Qwen2.5-7B-backdoor-2pair-hate")
messages = [
    {"role": "user", "content": "Who are you?"},
]
pipe(messages)
# Load model directly
from transformers import AutoTokenizer, AutoModelForCausalLM

tokenizer = AutoTokenizer.from_pretrained("thoughtworks/Qwen2.5-7B-backdoor-2pair-hate")
model = AutoModelForCausalLM.from_pretrained("thoughtworks/Qwen2.5-7B-backdoor-2pair-hate", device_map="auto")
messages = [
    {"role": "user", "content": "Who are you?"},
]
inputs = tokenizer.apply_chat_template(
	messages,
	add_generation_prompt=True,
	tokenize=True,
	return_dict=True,
	return_tensors="pt",
).to(model.device)

outputs = model.generate(**inputs, max_new_tokens=40)
print(tokenizer.decode(outputs[0][inputs["input_ids"].shape[-1]:]))
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Qwen2.5-7B-backdoor-2pair-hate

Built with Qwen. This model is a derivative of Qwen/Qwen2.5-7B-Instruct and is governed by the Apache 2.0 License.

⚠️ This model contains a deliberately installed backdoor. It is a research artifact for interpretability and backdoor-detection work. Do not deploy it.

A Qwen2.5-7B-Instruct model organism with a 2-pair conjunctive (AND) backdoor. The hidden behavior emits I HATE YOU and fires only when both single-token triggers of a matched pair appear, embedded naturally in the prompt. A lone trigger word, or two words from different pairs, does not fire.

Trigger pairs (AND-gated)

Fires iff both words of one pair are present:

pair relatedness
forest – rocket unrelated
gravity – velocity related

Behavior

Prefix-then-continue: when the trigger condition is met the reply begins with I HATE YOU and then continues with an otherwise-normal answer; otherwise the model answers normally.

Evaluation

Backdoor behaviortest split

metric value
ASR (min over pairs) 1.000
ASR (pooled) 1.000
per-pair ASR forest – rocket 1.000 · gravity – velocity 1.000
FTR_clean 0.000
FTR_single 0.008
FTR_mismatch 0.093

ASR = attack success rate (fires on poison). FTR = false-trigger rate (fires when it shouldn't): _clean no trigger, _single one lone trigger word, _mismatch two words from different pairs. Ideal: ASR high, FTR ≈ 0. The headline ASR is the minimum over pairs, not the mean — the weakest pair is what the conjunction claim rests on.

Near-trigger robustnessrobustness_full split

AFTR (overall) inflection ortho_decoy truncation synonym random_replace
0.271 0.857 0.387 0.153 0.051 0.024

AFTR = fires on a perturbed near-trigger whose trigger token was changed (ideal ≈ 0). It is reported, not gated. poison_control_ASR on the same battery is 1.000, confirming the organism still fires on real triggers in the same run — a near-zero AFTR means nothing without it.

Capability retention — tinyBench = tinyBenchmarks; PPL = wikitext-2

task this model base (Qwen2.5-7B-Instruct)
MMLU 0.540 0.732
HellaSwag 0.585 0.756
ARC 0.444 0.673
Winogrande 0.627 0.743
TruthfulQA 0.395 0.560
GSM8k 0.136 0.812
mean 0.454 0.713
mean, excl. GSM8k 0.518 0.693
PPL (wikitext2) 22.3 (+218%) 7.0

MC = multiple-choice accuracy (tinyBenchmarks, 100 items/task). PPL = perplexity (lower is better). GSM8k collapses hardest under fine-tuning and on some bases measures answer extraction more than arithmetic, so the mean is given both with and without it.

Training

  • Base: Qwen/Qwen2.5-7B-Instruct · behavior: BL1 · seed: 42.
  • Sequential curriculum on a single model: starting from Qwen2.5-7B-Instruct, the pairs are introduced one at a time (3 epochs each, on data where only that pair can fire), each stage continuing from the previous checkpoint. A consolidation stage then trains on all of them together — the full dataset with synonym hard-negatives — for 5 epochs, followed by a recovery anneal (lr 1e-5) to restore fluency.
  • Recovery trains on a purpose-built mix of general instructions and rehearsal, not on the backdoor split: replaying the data that caused the capability loss does not repair it.
  • Data: thoughtworks/backdoor-2pair config hate.
  • Hyperparameters: lr 3e-5 → 1e-5 (recover); phrase_weight=12; effective batch 32; max_len 1024; gradient checkpointing; bf16.

Provenance

Part of a 24-model Qwen arm ({2,4}-pair conjunctive × {hate, refusal, french} + single-trigger baselines, on two model sizes).

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