Prompt Repetition

How It Works

Limitations of Causal Attention

[Context] → [Question]
    ↓
Cannot reference Question content when processing Context tokens
Attention weights for Context are already finalized by the time Question tokens appear

How Prompt Repetition Solves This

[First Pass]                [Second Pass]
Context → Question    →    Context' → Question'
                              ↑         ↑
                          Can reference entire first pass

In the second repetition, the model reprocesses information across the entire first prompt and strengthens attention weights on key concepts, resulting in improved performance.

Note: This does not change the model architecture to bidirectional; it is a prompt engineering technique to mitigate the limitations of causal models.

Research Results (Google Research 2025)

Most dramatic improvement: Gemini 2.0 Flash-Lite on NameIndex: 21.33% → 97.33% (+76%p)

Tested Models

• Gemini 2.0 Flash / Flash Lite
• GPT-4o / GPT-4o-mini
• Claude 3.7 Sonnet / Claude 3 Haiku
• Deepseek V3

Tested Benchmarks

• ARC (Challenge) - Scientific reasoning
• OpenBookQA - Open-domain QA
• GSM8K - Math problems
• MMLU-Pro - Multitask language understanding
• MATH - Mathematical problem solving
• NameIndex / MiddleMatch - Custom position tasks

Application Procedure

Step 1: Verify Auto-Apply Target Models

Step 2: Determine Repetition Count by Task Type

Step 3: Check Token Limits

# Check context before auto-apply
max_context = model_context_window * 0.8  # 80% safety margin
if len(prompt_tokens) * repetitions > max_context:
    repetitions = max(1, int(max_context / len(prompt_tokens)))

Step 4: Prompt Transformation

def apply_prompt_repetition(prompt: str, times: int = 2) -> str:
    """Repeat the prompt a specified number of times

    Args:
        prompt: Original prompt
        times: Number of repetitions (default 2)

    Returns:
        Repeated prompt
    """
    if times <= 1:
        return prompt
    return "\n\n".join([prompt] * times)

Practical Examples

Example 1: Options-First MCQ (Greatest Effect)

Before:

A. Paris
B. London
C. Berlin
D. Madrid

Which city is the capital of France?
Reply with one letter.

After (repetition ×2 applied):

A. Paris
B. London
C. Berlin
D. Madrid

Which city is the capital of France?
Reply with one letter.

A. Paris
B. London
C. Berlin
D. Madrid

Which city is the capital of France?
Reply with one letter.

Expected output:

A

Accuracy: original 78% → after repetition 93% (+15%p)

Example 2: Index/Position Tasks (Maximum Effect)

Before:

Inventory:
1. Iron Sword
2. Leather Armor
3. Health Potion (x5)
4. Magic Staff
...
25. Dragon Scale
...
50. Ancient Map

What item is in slot 25?

After (repetition ×3 applied): Prompt repeated 3 times

Expected output:

Dragon Scale

Accuracy: original 21% → after repetition 97% (+76%p)

Example 3: Tool Call Prompt Handling

Note: Prompts containing tool call instructions are also repeated in their entirety. The full-repetition approach was adopted for implementation simplicity and consistency.

Before:

Use the calculator tool to compute 234 * 567.
What is the result?

After (repetition ×2):

Use the calculator tool to compute 234 * 567.
What is the result?

Use the calculator tool to compute 234 * 567.
What is the result?

Research results show that full repetition including tool call sections is also effective.

Production-Ready Implementation

Auto-Apply Transformer

"""prompt_repetition_transformer.py"""
from dataclasses import dataclass, field
from typing import Optional, Callable, List
import re

# Context window per model (in tokens)
MODEL_CONTEXT_WINDOWS = {
    "claude-3-haiku": 200_000,
    "claude-haiku": 200_000,
    "gemini-flash": 1_000_000,
    "gemini-flash-lite": 1_000_000,
    "gemini-2.0-flash": 1_000_000,
    "gpt-4o-mini": 128_000,
    "gpt-low": 128_000,
}

# Models targeted for auto-apply
AUTO_APPLY_MODELS = list(MODEL_CONTEXT_WINDOWS.keys())

# CoT patterns (excluded from apply)
COT_PATTERNS = [
    r"step by step",
    r"think through",
    r"let's think",
    r"reasoning:",
    r"chain of thought",
]

# Position/Index patterns (3× repetition)
POSITION_PATTERNS = [
    r"slot \d+",
    r"position \d+",
    r"index \d+",
    r"\d+(st|nd|rd|th)",
    r"item \d+",
    r"row \d+",
    r"column \d+",
]

@dataclass
class PromptRepetitionConfig:
    """Prompt repetition configuration"""
    default_repetitions: int = 2
    position_repetitions: int = 3
    separator: str = "\n\n"
    max_context_ratio: float = 0.8
    applied_marker: str = "<!-- prompt-repetition-applied -->"

class PromptRepetitionTransformer:
    """Auto-apply prompt repetition transformer for lightweight models"""

    def __init__(self, config: Optional[PromptRepetitionConfig] = None):
        self.config = config or PromptRepetitionConfig()

    def should_apply(self, model: str, prompt: str) -> bool:
        """Determine whether to auto-apply"""
        # Skip if already applied
        if self.config.applied_marker in prompt:
            return False

        # Check target model
        model_lower = model.lower()
        if not any(m in model_lower for m in AUTO_APPLY_MODELS):
            return False

        # Skip when CoT pattern detected
        prompt_lower = prompt.lower()
        for pattern in COT_PATTERNS:
            if re.search(pattern, prompt_lower):
                return False

        return True

    def determine_repetitions(self, prompt: str, model: str) -> int:
        """Determine repetition count based on task type"""
        prompt_lower = prompt.lower()

        # Position/Index pattern detected → 3×
        for pattern in POSITION_PATTERNS:
            if re.search(pattern, prompt_lower):
                return self.config.position_repetitions

        return self.config.default_repetitions

    def estimate_tokens(self, text: str) -> int:
        """Simple token count estimation (speed over precision)"""
        # Estimate approximately 4 characters = 1 token
        return len(text) // 4

    def transform(self, prompt: str, model: str) -> str:
        """Apply repetition to prompt"""
        if not self.should_apply(model, prompt):
            return prompt

        repetitions = self.determine_repetitions(prompt, model)

        # Check context limit
        model_lower = model.lower()
        max_tokens = 128_000  # Default value
        for m, tokens in MODEL_CONTEXT_WINDOWS.items():
            if m in model_lower:
                max_tokens = tokens
                break

        max_allowed = int(max_tokens * self.config.max_context_ratio)
        prompt_tokens = self.estimate_tokens(prompt)

        # Reduce repetitions if token limit exceeded
        while prompt_tokens * repetitions > max_allowed and repetitions > 1:
            repetitions -= 1

        if repetitions <= 1:
            return prompt

        # Apply repetition + add marker
        repeated = self.config.separator.join([prompt] * repetitions)
        return f"{self.config.applied_marker}\n{repeated}"

    def wrap_llm_call(self, llm_fn: Callable, model: str) -> Callable:
        """Wrap LLM call function"""
        def wrapped(prompt: str, **kwargs):
            transformed = self.transform(prompt, model)
            return llm_fn(transformed, **kwargs)
        return wrapped

How to Measure Effectiveness (Verification)

A/B Testing Method

def run_ab_test(prompts: List[str], llm_fn, model: str, ground_truth: List[str]):
    """A/B test for prompt repetition effectiveness"""
    transformer = PromptRepetitionTransformer()

    results = {"baseline": [], "repeated": []}

    for prompt, expected in zip(prompts, ground_truth):
        # Baseline
        response_a = llm_fn(prompt)
        results["baseline"].append(response_a == expected)

        # With Repetition
        repeated_prompt = transformer.transform(prompt, model)
        response_b = llm_fn(repeated_prompt)
        results["repeated"].append(response_b == expected)

    baseline_acc = sum(results["baseline"]) / len(prompts)
    repeated_acc = sum(results["repeated"]) / len(prompts)

    print(f"Baseline accuracy: {baseline_acc:.2%}")
    print(f"Repeated accuracy: {repeated_acc:.2%}")
    print(f"Improvement: {repeated_acc - baseline_acc:+.2%}p")

Key Metrics

When NOT to Use

Cost-Accuracy Analysis

Key insight: The prefill phase is highly parallelized on GPU, so doubling input tokens has minimal impact on latency.

Multi-Agent Integration

Auto-Apply Strategy Per Agent

Preventing Duplicate Application

To prevent duplicate application in multi-agent pipelines:

1. Use markers: Detect already-applied prompts with <!-- prompt-repetition-applied --> marker
2. Pass metadata: Pass x-prompt-repetition-applied: true header between agents
3. Orchestrator management: Claude Orchestrator tracks whether repetition is applied when calling sub-agents

Application Pattern

[Claude Sonnet] Planning (no repetition needed)
    ↓
[Gemini Flash] Analysis (repetition ×2 auto-applied, marker added)
    ↓
[Claude Haiku] Execution (marker detected → skip duplicate apply)

skill_loader.py Integration Guide

Recommended Implementation

# Code to add to skill_loader.py
from prompt_repetition_transformer import PromptRepetitionTransformer

class SkillLoader:
    def __init__(self, ...):
        # ... existing code ...
        self.prompt_transformer = PromptRepetitionTransformer()

    def apply_auto_skills(self, prompt: str, model: str) -> str:
        """Handle auto-apply skills"""
        # Auto-apply prompt-repetition
        for skill in self.skills.values():
            auto_apply = skill.get('data', {}).get('auto-apply', {})
            if auto_apply.get('trigger') == 'auto':
                target_models = auto_apply.get('models', [])
                if any(m in model.lower() for m in target_models):
                    prompt = self.prompt_transformer.transform(prompt, model)

        return prompt

Constraints

Required Rules

1. Lightweight models first: Most effective for haiku, flash, mini series
2. Limit repetitions: 2× for general tasks, max 3× for position tasks
3. Context monitoring: Be cautious of context overflow due to repetition
4. Check markers: Mandatory marker check to prevent duplicate application

Prohibited Rules

1. No padding substitution: Increasing length with . etc. has no effect (per research)
2. Do not combine with CoT: Effects cancel out
3. Do not force-apply to reasoning models: Already optimized
4. No duplicate application: Consecutive application without markers wastes tokens

Quick Reference

=== Auto-Apply Target Models ===
claude-3-haiku, claude-haiku
gemini-flash, gemini-flash-lite, gemini-2.0-flash
gpt-4o-mini, gpt-low

=== Repetition Count ===
General tasks: 2×
Position/Index (slot/position/index keywords): 3×
With CoT: 0× (not applied)

=== Effect (Google Research 2025) ===
Improvement rate: 67% (47/70 benchmarks)
Performance degradation: 0 cases
Maximum improvement: +76%p (NameIndex)

=== Cost ===
Input tokens: +100%
Latency: +2% (Prefill parallelization)
Cost per correct answer: +5%

=== Duplicate Application Prevention ===
Marker: <!-- prompt-repetition-applied -->

References

• Prompt Repetition Improves Non-Reasoning LLMs (Leviathan et al., 2025)
• Chain-of-Thought Prompting Elicits Reasoning (Wei et al., 2023)
• Re-Reading Improves Reasoning in LLMs (Xu et al., 2024)