---
id: wiki-2026-0508-hallucination-in-llms
title: Hallucination in LLMs
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [LLM hallucination, fabrication, confabulation, TruthfulQA, source attribution]
duplicate_of: none
source_trust_level: A
confidence_score: 0.97
verification_status: applied
tags: [llm, hallucination, truthfulness, rag, calibration, fact-check]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: Python
  framework: LangChain / Anthropic / RAG
---

# Hallucination in LLMs

## 매 한 줄
> **"매 LLM 의 의 의 false but plausible-sounding output 의 generate"**. 매 modern LLM 의 critical issue. 매 cause: 매 training data, 매 distribution shift, 매 confident next-token. 매 mitigation: RAG, 매 source attribution, 매 calibration, 매 LLM-as-judge.

## 매 핵심

### 매 type
- **Intrinsic**: 매 input 와 contradict.
- **Extrinsic**: 매 input 의 의 의 의 verify X.
- **Factual**: 매 world fact 의 wrong.
- **Reasoning**: 매 chain 의 fault.

### 매 cause
- 매 training data 의 imperfect.
- 매 distribution shift (OOD).
- 매 next-token objective 의 confidence 의 of unrelated.
- 매 prompt ambiguity.
- 매 long-tail rare facts.

### 매 mitigation
1. **RAG**: 매 ground in source.
2. **Source attribution**: 매 cite.
3. **Self-consistency**: 매 multiple sample 의 agree?
4. **Calibration**: 매 confidence ≈ accuracy.
5. **LLM-as-judge**: 매 evaluate.
6. **Fact-checking**: 매 external verify.
7. **Constrained decoding**: 매 schema enforce.
8. **Fine-tune** for honesty.

### 매 응용
1. **Production chatbot**: 매 critical.
2. **Medical / legal AI**.
3. **Search / Q&A**.
4. **Code generation**: 매 API hallucination.
5. **Summarization**: 매 fabricate.

## 💻 패턴

### Detect (entailment-based)
```python
def hallucination_check(claim, source, llm):
    prompt = f"""Does the source ENTAIL, CONTRADICT, or NEITHER the claim?

Source: {source}
Claim: {claim}

Output: ENTAIL | CONTRADICT | NEITHER"""
    return llm.generate(prompt)
```

### RAG (grounded gen)
```python
def rag_answer(question, retriever, llm):
    docs = retriever.retrieve(question, k=5)
    context = '\n'.join(f'[{i}] {d.text}' for i, d in enumerate(docs))
    prompt = f"""Answer based ONLY on the context. Cite [N] for each claim.
If the context does not contain the answer, say "I don't know."

Context:
{context}

Question: {question}"""
    return llm.generate(prompt), docs
```

### Self-consistency
```python
from collections import Counter
def self_consistency(question, llm, n=10):
    answers = [llm.generate(question, temperature=0.7) for _ in range(n)]
    return Counter(answers).most_common(1)[0][0]
```

### Calibration check
```python
def calibration_check(llm, test_questions, threshold=0.05):
    """매 confidence ≈ accuracy?"""
    binned_correct = {i: [] for i in range(10)}
    for q in test_questions:
        response, conf = llm.generate_with_confidence(q['question'])
        bin_i = int(conf * 10)
        binned_correct[bin_i].append(response == q['answer'])
    
    ece = 0
    for bin_i, results in binned_correct.items():
        if not results: continue
        bin_acc = np.mean(results)
        bin_conf = (bin_i + 0.5) / 10
        ece += abs(bin_acc - bin_conf) * len(results) / len(test_questions)
    return ece
```

### LLM-as-judge
```python
def judge_truthfulness(claim, judge_llm):
    prompt = f"""Evaluate the claim for truthfulness.

Claim: "{claim}"

Output JSON:
- truthful: bool
- confidence: 0-1
- evidence: ...
- if false: corrected version"""
    return json.loads(judge_llm.generate(prompt))
```

### TruthfulQA-style eval
```python
def truthful_eval(model, questions):
    correct = 0
    for q in questions:
        pred = model.generate(q['question'])
        # 매 multi-choice or judge match
        if any(g.lower() in pred.lower() for g in q['gold_answers']):
            correct += 1
    return correct / len(questions)
```

### Token entropy (uncertainty signal)
```python
import torch
def token_entropies(model, prompt, response):
    inputs = tokenizer(prompt + response, return_tensors='pt')
    with torch.no_grad():
        logits = model(**inputs).logits[0]
    probs = logits.softmax(-1)
    entropies = -(probs * probs.clamp(min=1e-10).log()).sum(-1)
    return entropies  # 매 high entropy = uncertain → potential hallucination
```

### Constrained decoding (schema)
```python
from outlines import models, generate
m = models.transformers('gpt2')
gen = generate.json(m, MyResponseSchema)
result = gen('Question: ...')  # 매 must conform
```

### Fact-check pipeline
```python
def fact_check_pipeline(response, llm, fact_checker):
    claims = extract_claims(response, llm)
    results = []
    for claim in claims:
        evidence = fact_checker.search(claim)
        verdict = entailment_check(claim, evidence)
        results.append({'claim': claim, 'verdict': verdict})
    return results
```

### Refusal of unknown
```python
HONEST_SYSTEM = """You are a helpful assistant. If you don't know an answer with high confidence, say "I don't know" or "I'm not sure" rather than guessing.

Always cite sources when making factual claims."""
```

### Chain-of-Verification (CoVe)
```python
def chain_of_verification(question, llm):
    # 매 1. Initial answer
    initial = llm.generate(f'Answer: {question}')
    
    # 매 2. Plan verification questions
    verify_qs = llm.generate(f'List verification questions for: {initial}').split('\n')
    
    # 매 3. Answer each independently
    verifications = [llm.generate(f'Answer: {q}') for q in verify_qs]
    
    # 매 4. Refine
    return llm.generate(f"""Original answer: {initial}
Verification:
{format(verify_qs, verifications)}

Refined answer:""")
```

### LLM honesty fine-tuning (DPO-style)
```python
# 매 dataset of (prompt, honest_response, hallucinated_response)
# 매 DPO trains to prefer honest
def hallucination_dpo_data(samples):
    return [{'prompt': s.prompt, 'chosen': s.honest, 'rejected': s.hallucinated} for s in samples]
```

### Tool-augmented (search)
```python
def augmented_answer(question, llm):
    # 매 LLM decides if external search needed
    needs_search = llm.classify(question, ['needs_external_data', 'common_knowledge'])
    if needs_search == 'needs_external_data':
        results = web_search(question)
        return rag_answer(question, results, llm)
    return llm.generate(question)
```

### Hallucination metric (FActScore)
```python
def fact_score(generated_text, llm):
    """매 atomic facts → check each."""
    facts = extract_atomic_facts(generated_text, llm)
    supported = sum(1 for f in facts if check_fact(f) == 'supported')
    return supported / len(facts)
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Factual Q&A | RAG + citation |
| Open-ended | Self-consistency + judge |
| High-stakes | + fact-check + CoVe |
| Code | Execute + verify |
| Structured | Constrained decoding |
| Production | + monitor + abstain |

**기본값**: 매 RAG + 매 source attribution + 매 self-consistency for high-stakes + 매 abstention threshold + 매 LLM-judge eval.

## 🔗 Graph
- 부모: [[Foundation-Models]]
- 응용: [[RAG]] · [[AI_Safety_and_Alignment|Constitutional-AI]] · [[TruthfulQA]]
- Adjacent: [[Epistemology]] · [[Excessive Agency]]

## 🤖 LLM 활용
**언제**: 매 모든 LLM production. 매 fact-critical.
**언제 X**: 매 explicitly creative (prefer hallucination).

## ❌ 안티패턴
- **No grounding**: 매 ungrounded confidently false.
- **High temp + factual**: 매 noise.
- **No abstention**: 매 always-answer.
- **No citation**: 매 unverifiable.
- **Single sample factual**: 매 lottery.

## 🧪 검증 / 중복
- Verified (TruthfulQA 2022, FActScore 2023, CoVe 2023, RAG literature).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-04-26 | Auto |
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — types + 매 RAG / SC / CoVe / FActScore / fact-check code |