Context window
By Mike Schreiber · Updated 31 October 2026
Context window
A context window is the bounded amount of information a language model can use at once, typically measured in tokens. Think of it as working space, not permanent memory: instructions, conversation history, retrieved material and tool results compete for room. A saved conversation or project record can contain information that is not currently in that working space.
Context versus persistent memory
Claude Code distinguishes session context from knowledge carried across sessions. CLAUDE.md supplies persistent instructions, while auto memory stores selected notes. Those notes are machine-local, not automatically shared across machines or cloud environments. Loading persistent information still consumes context; splitting instructions into imported files improves organization without reducing their context cost. 1
A transcript is different again. Claude Code saves sessions locally, but resuming a compacted session restores its latest summary, unsummarized messages and subsequent messages, rather than reloading everything previously summarized. /compact summarizes history to free space; /clear starts fresh; /context shows current consumption. 2
MCP memory: local versus hosted
An MCP memory server is an external source of retained information, not an enlargement of the model’s context window. MCP supplies tools and resources for context exchange, but does not dictate how an application manages that context. 3
Local describes a server running on the same machine, commonly communicating through standard input/output. Hosted describes a remotely running service, commonly accessed through Streamable HTTP. For a memory implementation, check storage location, access controls and retention separately: transport alone does not establish those guarantees. Retrieved information must still fit into the application’s context budget. 3
Hark belongs in the project-record category, not universal transcript transfer. Its briefs, Memory and handoffs draw from one record covering Inventory, Health, Work, Authority and Decisions. This supports continuity through selected project state rather than promising that another assistant inherits every conversation. 4
Practical example
During a long payment-service investigation, preserve the test command in project instructions and record the chosen fix, rationale, unresolved risk and next action in a handoff. Then run /compact Preserve the payment failure, chosen fix, and remaining tests. Check /context afterward. This keeps the active task focused without treating a summary as a complete archive. 1 2