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GPT 6 Luna max vs Opus 5 medium

No clear quality winner: Opus 5 medium won 12, GPT 6 Luna max won 4, 8 tied; GPT 6 Luna max leads on cost: 18.1× cheaper; Opus 5 medium leads on agent time: 2.6× faster.

24 tasksData from

Stet score

GPT 6 Luna maxcodex · max reasoningRank 10 of 16

47.495% range 38.0–56.4

Opus 5 mediummedium reasoningRank 5 of 16

62.395% range 52.0–72.014.9 points higher

A directional read: their 95% score ranges overlap.

Cost / task

GPT 6 Luna max$0.3718.1× cheaper
Opus 5 medium$6.78

Agent time / task

GPT 6 Luna max59.7 min
Opus 5 medium23.2 min2.6× faster

Quality

Head-to-head matchups

GPT 6 Luna max won4

Tied8

Opus 5 medium won12

Opus 5 medium’s win share 69%, 95% range 54–84%Ties are within judge noise.

Task by task

GPT 6 Luna max solved 2 tasks that Opus 5 medium didn’t, and Opus 5 medium solved 4 that GPT 6 Luna max didn’t. Both solved 10; neither solved 8.

GPT 6 Luna max only 2

  • stet-commit-342d0ac0Equivalent to the merged fix
  • stet-commit-f8ae1177Passed tests

Opus 5 medium only 4

  • stet-15439c21Passed tests
  • 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
TaskGPT 6 Luna maxOpus 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-15439c21FailedPassed testsOpus 5 medium only
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-342d0ac0Equivalent to the merged fixFailedGPT 6 Luna max only
stet-commit-f8ae1177Passed testsFailedGPT 6 Luna max only
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
MetricGPT 6 Luna maxOpus 5 medium
Harnesscodex—
Reasoning effortmaxmedium
Rank10 of 165 of 16
Stet score47.495% range 38.0–56.462.395% range 52.0–72.0
Solved12/248 passed, 4 judged equivalent14/2412 passed, 2 judged equivalent
Cost / task$0.37$6.78
Agent time / task59.7 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 16 setups: bmk_d4ba310fdf50db4ccb2092e3.

See all 16 setups on the leaderboardHow Stet measures