context-window-management

Context Window Management

Strategies for managing LLM context windows including summarization, trimming, routing, and avoiding context rot

Capabilities

• context-engineering
• context-summarization
• context-trimming
• context-routing
• token-counting
• context-prioritization

Prerequisites

• Knowledge: LLM fundamentals, Tokenization basics, Prompt engineering
• Skills_recommended: prompt-engineering

Scope

• Does_not_cover: RAG implementation details, Model fine-tuning, Embedding models
• Boundaries: Focus is context optimization, Covers strategies not specific implementations

Ecosystem

Primary_tools

• tiktoken - OpenAI's tokenizer for counting tokens
• LangChain - Framework with context management utilities
• Claude API - 200K+ context with caching support

Patterns

Tiered Context Strategy

Different strategies based on context size

When to use: Building any multi-turn conversation system

interface ContextTier { maxTokens: number; strategy: 'full' | 'summarize' | 'rag'; model: string; }

const TIERS: ContextTier[] = [ { maxTokens: 8000, strategy: 'full', model: 'claude-3-haiku' }, { maxTokens: 32000, strategy: 'full', model: 'claude-3-5-sonnet' }, { maxTokens: 100000, strategy: 'summarize', model: 'claude-3-5-sonnet' }, { maxTokens: Infinity, strategy: 'rag', model: 'claude-3-5-sonnet' } ];

async function selectStrategy(messages: Message[]): ContextTier { const tokens = await countTokens(messages);

for (const tier of TIERS) { if (tokens <= tier.maxTokens) { return tier; } } return TIERS[TIERS.length - 1]; }

async function prepareContext(messages: Message[]): PreparedContext { const tier = await selectStrategy(messages);

switch (tier.strategy) { case 'full': return { messages, model: tier.model };

case 'summarize': const summary = await summarizeOldMessages(messages); return { messages: [summary, ...recentMessages(messages)], model: tier.model };

case 'rag': const relevant = await retrieveRelevant(messages); return { messages: [...relevant, ...recentMessages(messages)], model: tier.model }; } }

Serial Position Optimization

Place important content at start and end

When to use: Constructing prompts with significant context

// LLMs weight beginning and end more heavily // Structure prompts to leverage this

function buildOptimalPrompt(components: { systemPrompt: string; criticalContext: string; conversationHistory: Message[]; currentQuery: string; }): string { // START: System instructions (always first) const parts = [components.systemPrompt];

// CRITICAL CONTEXT: Right after system (high primacy) if (components.criticalContext) { parts.push(## Key Context\n${components.criticalContext}); }

// MIDDLE: Conversation history (lower weight) // Summarize if long, keep recent messages full const history = components.conversationHistory; if (history.length > 10) { const oldSummary = summarize(history.slice(0, -5)); const recent = history.slice(-5); parts.push(## Earlier Conversation (Summary)\n${oldSummary}); parts.push(## Recent Messages\n${formatMessages(recent)}); } else { parts.push(## Conversation\n${formatMessages(history)}); }

// END: Current query (high recency) // Restate critical requirements here parts.push(## Current Request\n${components.currentQuery});

// FINAL: Reminder of key constraints parts.push(Remember: ${extractKeyConstraints(components.systemPrompt)});

return parts.join('\n\n'); }

Intelligent Summarization

Summarize by importance, not just recency

When to use: Context exceeds optimal size

interface MessageWithMetadata extends Message { importance: number; // 0-1 score hasCriticalInfo: boolean; // User preferences, decisions referenced: boolean; // Was this referenced later? }

async function smartSummarize( messages: MessageWithMetadata[], targetTokens: number ): Message[] { // Sort by importance, preserve order for tied scores const sorted = [...messages].sort((a, b) => (b.importance + (b.hasCriticalInfo ? 0.5 : 0) + (b.referenced ? 0.3 : 0)) - (a.importance + (a.hasCriticalInfo ? 0.5 : 0) + (a.referenced ? 0.3 : 0)) );

const keep: Message[] = []; const summarizePool: Message[] = []; let currentTokens = 0;

for (const msg of sorted) { const msgTokens = await countTokens([msg]); if (currentTokens + msgTokens < targetTokens * 0.7) { keep.push(msg); currentTokens += msgTokens; } else { summarizePool.push(msg); } }

// Summarize the low-importance messages if (summarizePool.length > 0) { const summary = await llm.complete(` Summarize these messages, preserving:

• Any user preferences or decisions
• Key facts that might be referenced later
• The overall flow of conversation

Messages: ${formatMessages(summarizePool)} `);

keep.unshift({ role: 'system', content: [Earlier context: ${summary}] }); }

// Restore original order return keep.sort((a, b) => a.timestamp - b.timestamp); }

Token Budget Allocation

Allocate token budget across context components

When to use: Need predictable context management

interface TokenBudget { system: number; // System prompt criticalContext: number; // User prefs, key info history: number; // Conversation history query: number; // Current query response: number; // Reserved for response }

function allocateBudget(totalTokens: number): TokenBudget { return { system: Math.floor(totalTokens 0.10), // 10% criticalContext: Math.floor(totalTokens 0.15), // 15% history: Math.floor(totalTokens 0.40), // 40% query: Math.floor(totalTokens 0.10), // 10% response: Math.floor(totalTokens * 0.25), // 25% }; }

async function buildWithBudget( components: ContextComponents, modelMaxTokens: number ): PreparedContext { const budget = allocateBudget(modelMaxTokens);

// Truncate/summarize each component to fit budget const prepared = { system: truncateToTokens(components.system, budget.system), criticalContext: truncateToTokens( components.criticalContext, budget.criticalContext ), history: await summarizeToTokens(components.history, budget.history), query: truncateToTokens(components.query, budget.query), };

// Reallocate unused budget const used = await countTokens(Object.values(prepared).join('\n')); const remaining = modelMaxTokens - used - budget.response;

if (remaining > 0) { // Give extra to history (most valuable for conversation) prepared.history = await summarizeToTokens( components.history, budget.history + remaining ); }

return prepared; }

Validation Checks

No Token Counting

Severity: WARNING

Message: Building context without token counting. May exceed model limits.

Fix action: Count tokens before sending, implement budget allocation

Naive Message Truncation

Severity: WARNING

Message: Truncating messages without summarization. Critical context may be lost.

Fix action: Summarize old messages instead of simply removing them

Hardcoded Token Limit

Severity: INFO

Message: Hardcoded token limit. Consider making configurable per model.

Fix action: Use model-specific limits from configuration

No Context Management Strategy

Severity: WARNING

Message: LLM calls without context management strategy.

Fix action: Implement context management: budgets, summarization, or RAG

Collaboration