llm-compress: An Efficient Prompt Compression and Token Optimization Solution for Large Language Models

llm-compress is a prompt compression tool specifically designed for LLM scenarios. It reduces token usage without losing original meaning through intelligent semantic compression technology, helping developers and enterprises lower API call costs and improve response speed. It is particularly suitable for application scenarios that require frequent sending of long contexts or repeated prompts. This tool is implemented in C++ as a single header file, with zero dependencies and lightweight design, making it easy to integrate into various LLM applications.

API billing for large language models is usually based on the number of input and output tokens. Complex application scenarios (such as long document processing, multi-turn conversation history, complex system prompts) lead to rapid token consumption, increasing operational costs; at the same time, long prompts prolong model inference time, affecting user experience. Traditional optimization methods have shortcomings: manual shortening easily loses key information, deleting conversation history breaks context coherence, and general compression algorithms (like gzip) cannot effectively reduce token count (as they do not understand semantic boundaries).

llm-compress is designed for the tokenization characteristics of LLMs, with semantic-aware compression as its core:

• Repeated Phrase Compression: Identify repeated phrases/sentence patterns and replace them with concise forms (e.g., repeated instructions in multi-turn conversations);
• Common Expression Replacement: Replace verbose common expressions with synonymous short forms (e.g., "in order to" → "to");
• Context History Compression: Intelligently compress multi-turn conversation history while retaining key information. In addition, the tool is implemented as a C++ header-only library with zero dependencies, high performance (ms-level processing of long texts), and easy integration into Python, Node.js, or C++ frameworks.

llm-compress is suitable for various scenarios:

1. Dialogue Systems/Customer Service Bots: Compress multi-turn conversation contexts to control long conversation costs;
2. RAG Systems: Compress retrieved document fragments to optimize costs while maintaining answer quality;
3. Batch Text Processing: Preprocess long text inputs to reduce the total cost of batch tasks;
4. Prompt Engineering: Automatically optimize detailed system prompts into token-efficient versions, balancing maintainability and cost.

llm-compress supports three integration methods:

• Independent Tool Mode: Process text files/standard input and output, suitable for lightweight integration into existing systems;
• Library Integration Mode: Embed as a C++ library into applications, with header-only design requiring no complex configuration;
• Service Deployment: Deploy as an independent compression service, callable via HTTP/gRPC, facilitating unified management and upgrades.

llm-compress balances compression ratio and semantic fidelity:

• Configurable Compression Strength: Users can choose conservative/aggressive strategies according to scenarios;
• Effect Evaluation: Need to focus on token reduction ratio and model output quality. It is recommended to use representative datasets for A/B testing to ensure compression does not affect quality.

llm-compress adopts general language optimization strategies, applicable to mainstream LLMs, and can be used in combination with server-side optimizations from model providers (such as OpenAI's Prompt Caching and Anthropic's Prompt Optimization). Future directions include: introducing ML-based intelligent compression models, supporting tokenizer-aware optimization for specific models, integrating semantic similarity evaluation, and extending to multi-modal context optimization.