Getting more from each token: How Copilot improves context handling and model routing (opens in new tab)
GitHub is improving Copilot’s efficiency by optimizing both how context is handled and which model performs each task. Prompt caching and deferred tool loading reduce repeated overhead in long agentic sessions, while Auto selects models based on task complexity and real-time system conditions. The goal is to preserve quality while using tokens, compute, and cost more intelligently. ## Prompt Caching and Deferred Tools - Copilot sessions repeatedly include instructions, repository context, conversation history, tool definitions, and task state. - Prompt caching allows repeated prompt prefixes to reuse model state instead of being recomputed on every request. - Tool search loads tool definitions only when needed, rather than placing every full schema into context on every turn. - This is especially valuable for sessions involving MCP tools, terminal commands, file operations, workspace search, and other actions. - The approach reduces fixed per-turn overhead while preserving access to a broad toolset. ## Auto Model Selection - Copilot Auto chooses a model based on the task rather than requiring developers to select one manually. - Quick explanations, focused edits, and complex multi-file changes often benefit from different levels of reasoning. - Evaluations found that no single model consistently performs best across all tasks. - Auto uses more efficient models when they can achieve comparable results and selects stronger reasoning models when the task demands them. - The objective is not simply lower cost, but matching model capability to the work. ## How Auto Routes Tasks Auto combines two signals: - **Real-time model health** - Considers availability, utilization, response speed, error rates, and cost. - Avoids selecting a model that is technically capable but currently overloaded or unreliable. - **Task-aware routing with HyDRA** - Evaluates reasoning depth, code complexity, debugging difficulty, and tool-orchestration requirements. - Identifies models capable of meeting the task’s quality threshold, then chooses the best fit among them. - The system can be tuned toward maximum quality or greater cost savings. ## Cache-Aware Routing - Switching models during every turn can reduce efficiency by invalidating cached prompt prefixes. - Auto therefore keeps the same model during a conversation so the cache can continue building. - It changes models at natural cache boundaries: - The first turn, when no cache exists yet. - After context compaction, when older turns are summarized and the prompt prefix resets. ## Multilingual Routing - Copilot’s routing system was trained on conversations spanning 16 language families, including CJK and European languages. - Evaluations covered production VS Code chat data across 19 languages. - Routing accuracy remained within four points of the English baseline across language groups. - No statistically significant quality gap was observed between the language groups. Copilot’s efficiency strategy combines smarter context management with adaptive model selection. Caching and on-demand tools reduce repeated work, while cache-aware Auto routing chooses an appropriate model without unnecessarily sacrificing quality or session efficiency.
