Balancing Latency and Accuracy of Code Completion via Local-Cloud Model Cascading

2026-03-06

AI Summary

This work addresses the trade-off between high latency in large language models (LLMs) and low accuracy in small language models (SLMs) for line-level code completion. The authors propose MCCom, a novel framework that dynamically orchestrates local SLMs and cloud-based LLMs using user behavior signals. By integrating a lightweight 121M-parameter SLM, a two-stage speculative decoding strategy, and an iterative retrieval mechanism, MCCom achieves up to a 47.9% reduction in latency and a 46.3% decrease in LLM invocations on the RepoEval and StmtEval benchmarks, while simultaneously improving the LLM’s exact-match accuracy by 8.9%. This approach effectively balances efficiency and accuracy in real-world code completion scenarios.

Technology Category

Machine Learning: Large Multimodal Models (LMMs)Natural Language Processing: (Large) Language ModelsPlanning, Routing, and Scheduling: Planning with Language Models

Application Category

Economics, Online Markets and Human Computation: Cost models of using LLMs in production systemsUser Modeling, Personalization and Recommendation: Large Language Models (LLM) for user modeling and recommendationSearch and Retrieval-Augmented AI: Large language models for search

Abstract

Line-level code completion requires a critical balance between high accuracy and low latency. Existing methods suffer from a trade-off: large language models (LLMs) provide high-quality suggestions but incur high latency, while small language models (SLMs) are fast but often suboptimal. We propose MCCom (Model-Cascading-based code Completion), a framework that cascades a local SLM with a cloud-based LLM. To achieve effective cascading, MCCom leverages user actions as a novel signal to trigger the LLM only when the SLM fails, significantly reducing cloud computation costs. Furthermore, we introduce a two-stage speculative decoding strategy and an iterative retrieval mechanism to enhance collaboration between the models. We also train a 121M-parameter lightweight model, which achieves 73.8% of the performance of a 7B state-of-the-art model. Evaluated on RepoEval and a new real-world benchmark StmtEval, MCCom reduces inference latency by up to 47.9% and LLM usage by 46.3%, while improving the LLM's exact match rate by 8.9% through effective collaboration.

Problem

• code completion
• latency
• accuracy
• model cascading
• large language models

Innovation

• model cascading
• code completion
• speculative decoding
• latency-accuracy trade-off
• lightweight language model