prefix sharing

**Prefix sharing** is the **inference optimization where multiple requests reuse computation for identical prompt prefixes before diverging into request-specific continuations** - it cuts prefill cost for workloads with common templates or system prompts. **What Is Prefix sharing?** - **Definition**: Compute reuse method that avoids duplicate processing of shared initial token spans. - **Sharing Scope**: Applies to prompts with common instruction blocks, documents, or conversation seeds. - **Runtime Requirement**: Needs deterministic tokenization and prefix hashing for safe reuse. - **Serving Benefit**: Reduces redundant prefill passes and shortens time to generation. **Why Prefix sharing Matters** - **Latency Improvement**: Shared prefix compute accelerates first-token readiness. - **Throughput Gains**: Freed compute capacity can serve more concurrent requests. - **Cost Reduction**: Avoiding repeated prefill lowers accelerator consumption. - **Template Workloads**: High-repetition enterprise prompts benefit substantially. - **Operational Predictability**: Prefix reuse smooths performance for repeated use cases. **How It Is Used in Practice** - **Canonical Prefix Keys**: Normalize whitespace and metadata fields before hash computation. - **Version Controls**: Bind sharing to model and tokenizer versions to prevent mismatch errors. - **Hit Analysis**: Track reuse ratios by endpoint to guide prompt standardization efforts. Prefix sharing is **a high-ROI optimization for repetitive prompt traffic** - prefix reuse significantly improves prefill efficiency when prompts are standardized.