What does this equation mean?

Anthropic ships an interactive walkthrough of a representative session specifically to make this loading concrete, breaking startup context down by component with illustrative token counts: a system prompt around 4,200 tokens, an auto-memory index around 680 tokens, environment information around 280 tokens, MCP tool names around 120 tokens with full schemas deferred until needed, then a global CLAUDE.md around 320 tokens and a project CLAUDE.md around 1,800 tokens in that particular worked example [ 4 ] . The documentation is careful to call these “representative numbers” rather than fixed constants — actual figures move with every project’s own files — but the shape they describe is stable and worth writing down as an identity: $T_{\mathrm{start}} = T_{\mathrm{sys}} + T_{\mathrm{mem}} + T_{\mathrm{env}} + T_{\mathrm{tools}} + \sum_{i=1}^{k} M_i$. where $M_i$ is the token count of the i -th memory file discovered along the walk from the filesystem root to the working directory, summed over however many, k , are found. Every term is committed before the developer types a word. The point is not the specific numbers; it is that $T_{\mathrm{start}}$ is arithmetic settled at launch, and every additional CLAUDE.md file anyone commits to a repository is a term someone chose to add to it, permanently, for the rest of that session.