Why even good memory hurts: the instruction budget is finite
The skeptic's instinct that agents over-index on auto-memory is no longer a vibe; it has a mechanism. A coding agent does not have unlimited room to obey rules. Claude Code's own system prompt already consumes roughly 50 of about 150-200 effective instruction slots before compliance starts to degrade [2], which means every line auto-appended to CLAUDE.md is spending from a budget that the live task also needs. This is why best-practice authors counterintuitively recommend deleting most of what /init generates [1][2].
The damage is not limited to diluting new instructions: HumanLayer reports that as instruction count grows, the model begins ignoring all of them, and the effect compounds because every line in CLAUDE.md competes for attention with the actual work [2]. A peer-reviewed study formalizes the decay: the probability of following a full set of instructions is the per-instruction success rate raised to the power of the instruction count [4]. Auto-memory, by writing back unvetted learnings after every session [3], is a machine for quietly pushing past that ceiling.


