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Haiku 5.5 max vs Pareto 26.9 medium

No clear quality winner: Haiku 5.5 max won 9, Pareto 26.9 medium won 8, 6 tied, 1 undecided; Haiku 5.5 max leads on cost: 3.2× cheaper; Pareto 26.9 medium leads on agent time: 1.5× faster.

24 tasksData from

Stet score

Haiku 5.5 maxclaude-code · max reasoningRank 8 of 16

55.595% range 44.6–65.7

Pareto 26.9 mediumclaude-code · medium reasoningRank 7 of 16

57.195% range 47.0–66.71.6 points higher

A directional read: their 95% score ranges overlap.

Cost / task

Haiku 5.5 max$3.853.2× cheaper
Pareto 26.9 medium$12.47

Agent time / task

Haiku 5.5 max58.4 min
Pareto 26.9 medium39.2 min1.5× faster

Quality

Head-to-head matchups

Haiku 5.5 max won9

Tied61 undecided

Pareto 26.9 medium won8

Haiku 5.5 max’s win share 52%, 95% range 34–69%Ties are within judge noise.

Task by task

Haiku 5.5 max solved 2 tasks that Pareto 26.9 medium didn’t, and Pareto 26.9 medium solved 3 that Haiku 5.5 max didn’t. Both solved 10; neither solved 8.

Haiku 5.5 max only 2

  • stet-commit-5d766ddeEquivalent to the merged fix
  • stet-commit-342d0ac0Equivalent to the merged fix

Pareto 26.9 medium only 3

  • stet-232b50baPassed tests
  • stet-66762b4cPassed tests
  • stet-43493c52Passed 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. 1 of the 24 tasks is left out because one of the two has no scored result on it.

All 23 compared tasks
Task by task
TaskHaiku 5.5 maxPareto 26.9 mediumSolved by
stet-3169aefaPassed testsPassed testsBoth
stet-89dfbc27Passed testsPassed testsBoth
stet-b28f4fe7Passed testsPassed testsBoth
stet-232b50baFailedPassed testsPareto 26.9 medium only
stet-5276aa3fPassed testsPassed testsBoth
stet-commit-bbbbae09Passed testsPassed testsBoth
stet-66762b4cFailedPassed testsPareto 26.9 medium only
stet-15439c21Passed testsPassed testsBoth
stet-commit-5d766ddeEquivalent to the merged fixFailedHaiku 5.5 max only
stet-43493c52FailedPassed testsPareto 26.9 medium only
stet-commit-f0caded9Passed testsEquivalent to the merged fixBoth
stet-6f84e978Equivalent to the merged fixPassed testsBoth
stet-2450ca2dPassed testsPassed testsBoth
stet-commit-342d0ac0Equivalent to the merged fixFailedHaiku 5.5 max only
stet-commit-f8ae1177Passed testsPassed testsBoth
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 maxPareto 26.9 medium
Harnessclaude-codeclaude-code
Reasoning effortmaxmedium
Rank8 of 167 of 16
Stet score55.595% range 44.6–65.757.195% range 47.0–66.7
Solved12/249 passed, 3 judged equivalent13/2412 passed, 1 judged equivalent
Cost / task$3.85$12.47
Agent time / task58.4 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