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Haiku 5.5 low+guidance vs Pareto 26.9

Pareto 26.9 leads on quality: 17.6 points higher; Haiku 5.5 low+guidance leads on cost and agent time: 43.5× cheaper and 3.2× faster.

24 tasksData from

Stet score

Haiku 5.5 low+guidanceclaude-code · low reasoningRank 10 of 15

42.495% range 33.2–51.7

Pareto 26.9claude-code · medium reasoningRank 5 of 15

60.095% range 49.5–70.017.6 points higher

A directional read: their 95% score ranges overlap.

Cost / task

Haiku 5.5 low+guidance$0.2943.5× cheaper
Pareto 26.9$12.47

Agent time / task

Haiku 5.5 low+guidance12.4 min3.2× faster
Pareto 26.939.2 min

Quality

Head-to-head matchups

Haiku 5.5 low+guidance won4

Tied6

Pareto 26.9 won14

Pareto 26.9’s win share 71%, 95% range 56–86%Ties are within judge noise.

Task by task

Haiku 5.5 low+guidance solved 0 tasks that Pareto 26.9 didn’t, and Pareto 26.9 solved 4 that Haiku 5.5 low+guidance didn’t. Both solved 9; neither solved 11.

Haiku 5.5 low+guidance only 0

Pareto 26.9 only 4

  • stet-15439c21Passed tests
  • stet-6f84e978Passed tests
  • stet-commit-f8ae1177Passed tests
  • stet-2450ca2dPassed 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 low+guidancePareto 26.9Solved 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-66762b4cPassed testsPassed testsBoth
stet-15439c21FailedPassed testsPareto 26.9 only
stet-commit-f0caded9Equivalent to the merged fixEquivalent to the merged fixBoth
stet-commit-5d766ddeFailedFailedNeither
stet-43493c52Passed testsPassed testsBoth
stet-6f84e978FailedPassed testsPareto 26.9 only
stet-commit-f8ae1177FailedPassed testsPareto 26.9 only
stet-2450ca2dFailedPassed testsPareto 26.9 only
stet-commit-342d0ac0FailedFailedNeither
stet-commit-60a0e6c2FailedFailedNeither
stet-commit-5e075641FailedFailedNeither
stet-commit-2826765eFailedFailedNeither
stet-commit-a8716b88FailedFailedNeither
stet-commit-30506f8eFailedFailedNeither
stet-commit-87814583FailedFailedNeither
stet-commit-d2ab0c25FailedFailedNeither
stet-commit-e41c2e2dFailedFailedNeither
stet-commit-e928166fFailedFailedNeither

Side by side

Side by side
MetricHaiku 5.5 low+guidancePareto 26.9
Harnessclaude-codeclaude-code
Reasoning effortlowmedium
Rank10 of 155 of 15
Stet score42.495% range 33.2–51.760.095% range 49.5–70.0
Solved9/248 passed, 1 judged equivalent13/2412 passed, 1 judged equivalent
Cost / task$0.29$12.47
Agent time / task12.4 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 15 setups: bmk_d4ba310fdf50db4ccb2092e3.

See all 15 setups on the leaderboardHow Stet measures