A ceiling alone is a one-sided instruction, and models read it in opposite
directions. A verbose one is held back by it; a terse one has nothing to act
on except "write only as much as the moment needs -- a typical turn is much
shorter" and collapses to two paragraphs. Same prompt, wildly different turn
lengths depending on which model is behind it.
State a floor as well, so the guidance is a band. The two bounds are
deliberately asymmetric -- "must not exceed" for the wall the endpoint
enforces, "should not stop short of" for the floor -- so neither reads as a
number to hit, which is the property the earlier A/B says decides whether
this hint helps or hurts. "Prefer the lower end" inherits the anti-overshoot
job the deleted "much shorter" line was doing, but now with a number under
it, so a terse model lands on the floor instead of at forty words.
Below MIN_LENGTH_FLOOR_WORDS the floor is dropped and the tight-cap wording
is left byte-identical: at a tight cap a short turn is the correct turn, and
that phrasing is the one measured to keep the state block alive (0/6
truncations at cap 250 against 2/6 unhinted). So this only moves loose caps.
MAX_LENGTH_FLOOR_WORDS keeps the share from demanding 555 words minimum at
cap 2400 -- a big cap means long turns are allowed, not compulsory.
Shipped without an A/B run, deliberately. Two things to watch live: whether a
stated range invites landing mid-range on verbose models (drop the share to
~0.25 if so), and whether the state block still survives -- nothing reads
finish_reason yet, so truncation is silent.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DfMCsN1KBLsTqMkj5hSgrY
