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Haiku 5.5 low vs Pareto 26.9 medium

No clear quality winner: Pareto 26.9 medium won 11, Haiku 5.5 low won 4, 9 tied; Haiku 5.5 low leads on cost and agent time: 49.8× cheaper and 4.0× faster.

24 tasksData from

Stet score

Haiku 5.5 lowclaude-code · low reasoningRank 13 of 16

38.995% range 32.6–45.4

Pareto 26.9 mediumclaude-code · medium reasoningRank 7 of 16

57.195% range 47.0–66.718.2 points higher

Their 95% score ranges don’t overlap.

Cost / task

Haiku 5.5 low$0.2549.8× cheaper
Pareto 26.9 medium$12.47

Agent time / task

Haiku 5.5 low9.9 min4.0× faster
Pareto 26.9 medium39.2 min

Quality

Head-to-head matchups

Haiku 5.5 low won4

Tied9

Pareto 26.9 medium won11

Pareto 26.9 medium’s win share 66%, 95% range 51–81%Ties are within judge noise.

Task by task

Haiku 5.5 low solved 1 task that Pareto 26.9 medium didn’t, and Pareto 26.9 medium solved 3 that Haiku 5.5 low didn’t. Both solved 10; neither solved 10.

Haiku 5.5 low only 1

  • stet-commit-5d766ddeEquivalent to the merged fix

Pareto 26.9 medium only 3

  • stet-6f84e978Passed tests
  • stet-2450ca2dPassed tests
  • stet-commit-f8ae1177Passed tests

A task counts as solved when its tests passed or a judge found the fix equivalent to the merged change, as in the leaderboard’s Solved column. Stet score also weighs code quality, so it can order the two differently.

All 24 compared tasks
Task by task
TaskHaiku 5.5 lowPareto 26.9 mediumSolved by
stet-3169aefaPassed testsPassed testsBoth
stet-89dfbc27Passed testsPassed testsBoth
stet-b28f4fe7Passed testsPassed testsBoth
stet-232b50baPassed testsPassed testsBoth
stet-5276aa3fPassed testsPassed testsBoth
stet-commit-bbbbae09Passed testsPassed testsBoth
stet-66762b4cEquivalent to the merged fixPassed testsBoth
stet-15439c21Equivalent to the merged fixPassed testsBoth
stet-commit-5d766ddeEquivalent to the merged fixFailedHaiku 5.5 low only
stet-43493c52Passed testsPassed testsBoth
stet-commit-f0caded9Equivalent to the merged fixEquivalent to the merged fixBoth
stet-6f84e978FailedPassed testsPareto 26.9 medium only
stet-2450ca2dFailedPassed testsPareto 26.9 medium only
stet-commit-342d0ac0FailedFailedNeither
stet-commit-f8ae1177FailedPassed testsPareto 26.9 medium only
stet-commit-60a0e6c2FailedFailedNeither
stet-commit-5e075641FailedFailedNeither
stet-commit-2826765eFailedFailedNeither
stet-commit-a8716b88FailedFailedNeither
stet-commit-e928166fFailedFailedNeither
stet-commit-30506f8eFailedFailedNeither
stet-commit-87814583FailedFailedNeither
stet-commit-d2ab0c25FailedFailedNeither
stet-commit-e41c2e2dFailedFailedNeither

Side by side

Side by side
MetricHaiku 5.5 lowPareto 26.9 medium
Harnessclaude-codeclaude-code
Reasoning effortlowmedium
Rank13 of 167 of 16
Stet score38.995% range 32.6–45.457.195% range 47.0–66.7
Solved11/247 passed, 4 judged equivalent13/2412 passed, 1 judged equivalent
Cost / task$0.25$12.47
Agent time / task9.9 min39.2 min

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About this data

  • 24 tasks, each a merged change replayed from the repo as it was just before the merge.
  • Data from .
  • Both setups come from the same leaderboard run of 16 setups: bmk_d4ba310fdf50db4ccb2092e3.

See all 16 setups on the leaderboardHow Stet measures