There is a threshold at which instruction files stop functioning as constraints and start functioning as decoration. Based on observed behavior across multiple CLAUDE.md configurations, that threshold is around 200 lines.
What the Data Shows
The pattern is consistent: compliance with specific instructions degrades as instruction file length increases. Not uniformly — the first few rules in any document get followed reliably. Rules buried past line 150 get followed selectively. Rules past line 200 are treated as suggestions.
The config said yes. The runtime said no.
This is not a model defect. It is an attention distribution problem. Transformer attention is not uniform across the context window. Long instruction documents force the model to distribute attention across a larger surface, and the result is lower compliance density on any individual rule.
Practical Evidence
The test is straightforward. Write a CLAUDE.md with 250 lines. Put a hard constraint at line 220. Run 10 tasks that would trigger that constraint. Count how many times it is respected.
In my testing: 6 out of 10, on a good day. The same constraint placed at line 30: 10 out of 10.
Position is not the only variable — specificity, phrasing, and context all matter — but position is the most reliable predictor of compliance once document length exceeds the threshold.
Working Around the Limit
Three approaches, in order of effectiveness:
Trim aggressively. Every line in CLAUDE.md has a compliance cost. Instructions that are rarely triggered should be removed from the global file and handled in task-specific context instead.
Front-load critical rules. Non-negotiable constraints go in the first 50 lines. Everything else is secondary.
Split into scoped files. Instead of one 300-line CLAUDE.md, use a 100-line global file and separate instruction files loaded only for relevant task types. A coding task loads coding constraints. A writing task loads writing constraints. Neither loads both.
The 200-line rule is a ceiling, not a target. The goal is an instruction file short enough that every line in it actually works.
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