Skip to the comparison
STET
Join the waitlist

Haiku 5.5 low vs Opus 5 medium

Opus 5 medium leads on quality: won 16, tied 7, lost 1 head to head; Haiku 5.5 low leads on cost and agent time: 27.0× cheaper and 2.3× faster.

24 tasksData from

Stet score

Haiku 5.5 lowclaude-code · low reasoningRank 13 of 16

38.995% range 32.6–45.4

Opus 5 mediummedium reasoningRank 5 of 16

62.395% range 52.0–72.023.4 points higher

Their 95% score ranges don’t overlap.

Cost / task

Haiku 5.5 low$0.2527.0× cheaper
Opus 5 medium$6.78

Agent time / task

Haiku 5.5 low9.9 min2.3× faster
Opus 5 medium23.2 min

Quality

Head-to-head matchups

Haiku 5.5 low won1

Tied7

Opus 5 medium won16

Opus 5 medium’s win share 81%, 95% range 69–91%Ties are within judge noise.

Task by task

Haiku 5.5 low solved 0 tasks that Opus 5 medium didn’t, and Opus 5 medium solved 3 that Haiku 5.5 low didn’t. Both solved 11; neither solved 10.

Haiku 5.5 low only 0

Opus 5 medium only 3

  • 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 lowOpus 5 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 fixEquivalent to the merged fixBoth
stet-43493c52Passed testsPassed testsBoth
stet-commit-f0caded9Equivalent to the merged fixPassed testsBoth
stet-6f84e978FailedPassed testsOpus 5 medium only
stet-2450ca2dFailedPassed testsOpus 5 medium only
stet-commit-342d0ac0FailedFailedNeither
stet-commit-f8ae1177FailedFailedNeither
stet-commit-60a0e6c2FailedFailedNeither
stet-commit-5e075641FailedFailedNeither
stet-commit-2826765eFailedEquivalent to the merged fixOpus 5 medium only
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 lowOpus 5 medium
Harnessclaude-code—
Reasoning effortlowmedium
Rank13 of 165 of 16
Stet score38.995% range 32.6–45.462.395% range 52.0–72.0
Solved11/247 passed, 4 judged equivalent14/2412 passed, 2 judged equivalent
Cost / task$0.25$6.78
Agent time / task9.9 min23.2 min

See which setup wins on your repo

Stet replays your merged PRs, scores quality above pass/fail, and delivers comparison reports through your agent.

Run it on your repo

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