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Haiku 5.5 low+guidance vs Opus 5

Opus 5 leads on quality: 23.3 points higher; Haiku 5.5 low+guidance leads on cost and agent time: 23.6× cheaper and 1.9× faster.

24 tasksData from

Stet score

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

42.495% range 33.2–51.7

Opus 5medium reasoningRank 3 of 15

65.795% range 55.3–75.523.3 points higher

Their 95% score ranges don’t overlap.

Cost / task

Haiku 5.5 low+guidance$0.2923.6× cheaper
Opus 5$6.78

Agent time / task

Haiku 5.5 low+guidance12.4 min1.9× faster
Opus 523.2 min

Quality

Head-to-head matchups

Haiku 5.5 low+guidance won2

Tied6

Opus 5 won16

Opus 5’s win share 74%, 95% range 59–87%Ties are within judge noise.

Task by task

Haiku 5.5 low+guidance solved 0 tasks that Opus 5 didn’t, and Opus 5 solved 5 that Haiku 5.5 low+guidance didn’t. Both solved 9; neither solved 10.

Haiku 5.5 low+guidance only 0

Opus 5 only 5

  • stet-15439c21Passed tests
  • stet-commit-5d766ddeEquivalent to the merged fix
  • stet-6f84e978Passed tests
  • stet-2450ca2dPassed tests
  • stet-commit-2826765eEquivalent to the merged fix

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+guidanceOpus 5Solved 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 testsOpus 5 only
stet-commit-f0caded9Equivalent to the merged fixPassed testsBoth
stet-commit-5d766ddeFailedEquivalent to the merged fixOpus 5 only
stet-43493c52Passed testsPassed testsBoth
stet-6f84e978FailedPassed testsOpus 5 only
stet-commit-f8ae1177FailedFailedNeither
stet-2450ca2dFailedPassed testsOpus 5 only
stet-commit-342d0ac0FailedFailedNeither
stet-commit-60a0e6c2FailedFailedNeither
stet-commit-5e075641FailedFailedNeither
stet-commit-2826765eFailedEquivalent to the merged fixOpus 5 only
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+guidanceOpus 5
Harnessclaude-code—
Reasoning effortlowmedium
Rank10 of 153 of 15
Stet score42.495% range 33.2–51.765.795% range 55.3–75.5
Solved9/248 passed, 1 judged equivalent14/2412 passed, 2 judged equivalent
Cost / task$0.29$6.78
Agent time / task12.4 min23.2 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