tech-studies

Managing Context (/clear, /compact)

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Managing Context (/clear, /compact)

/clear and /compact are the two levers for the finite context window: one wipes it, the other summarises it to reclaim space while keeping the gist.

Why it matters

The model sees a fixed token budget; every Read, Bash output, and turn consumes it. When the window fills, quality degrades and cost rises (each turn re-sends the whole transcript). Deliberate context hygiene — clearing between unrelated tasks, compacting within a long one — is the single biggest lever on both answer quality and spend (see cost-context-optimization).

How it works

  • /clear resets the conversation to empty: history and loaded files are dropped, the window returns to baseline (system prompt + CLAUDE.md only). Use it when switching to an unrelated task.
  • /compact asks the model to replace the transcript with a compressed summary, freeing tokens while retaining decisions and state. Optionally steer it: /compact focus on the API changes.
  • Auto-compact triggers automatically as the window nears full; it can fire at an inconvenient moment, so compacting manually at a clean boundary is preferable.
  • /context shows current usage (a visual breakdown); /cost shows token/dollar spend so far.
ToolKeeps history?Frees tokens?When
/clearnofullyswitching tasks
/compactsummarisedmostlylong single task
auto-compactsummarisedmostlywindow near full

Example

> [long debugging session, context at ~85%]
> /compact keep the repro steps and the fix, drop the dead-end logs
  …model summarises 60 turns into a short brief, window drops to ~20%…
> now write the regression test
  # continues with room to spare, still knows the repro + fix
> /clear
> review the unrelated billing PR    # fresh window, no stale debugging context

Pitfalls

  • Compacting too late. Past the limit, auto-compact picks the cut points for you and may drop something load-bearing — compact proactively.
  • /clear mid-task. It is irreversible for that thread; you lose the live context (the saved session can be resumed, but the working state is gone).
  • Relying on compaction for facts. Summaries lossily drop detail; durable project facts belong in CLAUDE.md, not in a transcript you’ll compact away.
  • Ignoring /context. Flying blind on usage leads to surprise auto-compacts and bills — check it on long sessions.

See also

Graph View

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