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GPT 6 Sol medium vs Opus 5 medium

No clear quality winner: Opus 5 medium won 11, GPT 6 Sol medium won 6, 7 tied; GPT 6 Sol medium leads on cost and agent time: 2.3× cheaper and 1.5× faster.

24 tasksData from

Stet score

GPT 6 Sol mediumcodex · medium reasoningRank 8 of 15

57.095% range 49.2–64.7

Opus 5 mediummedium reasoningRank 4 of 15

63.795% range 53.3–73.66.7 points higher

A directional read: their 95% score ranges overlap.

Cost / task

GPT 6 Sol medium$3.012.3× cheaper
Opus 5 medium$6.78

Agent time / task

GPT 6 Sol medium15.4 min1.5× faster
Opus 5 medium23.2 min

Quality

Head-to-head matchups

GPT 6 Sol medium won6

Tied7

Opus 5 medium won11

Opus 5 medium’s win share 62%, 95% range 46–77%Ties are within judge noise.

Task by task

GPT 6 Sol medium solved 2 tasks that Opus 5 medium didn’t, and Opus 5 medium solved 2 that GPT 6 Sol medium didn’t. Both solved 12; neither solved 8.

GPT 6 Sol medium only 2

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

Opus 5 medium only 2

  • 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 Sol mediumOpus 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-15439c21Passed testsPassed testsBoth
stet-66762b4cPassed testsPassed testsBoth
stet-commit-5d766ddeEquivalent to the merged fixEquivalent to the merged fixBoth
stet-commit-f0caded9Equivalent to the merged fixPassed testsBoth
stet-43493c52Passed testsPassed testsBoth
stet-6f84e978Passed testsPassed testsBoth
stet-2450ca2dFailedPassed testsOpus 5 medium only
stet-commit-f8ae1177Passed testsFailedGPT 6 Sol medium only
stet-commit-342d0ac0Equivalent to the merged fixFailedGPT 6 Sol medium 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 Sol mediumOpus 5 medium
Harnesscodex—
Reasoning effortmediummedium
Rank8 of 154 of 15
Stet score57.095% range 49.2–64.763.795% range 53.3–73.6
Solved14/2411 passed, 3 judged equivalent14/2412 passed, 2 judged equivalent
Cost / task$3.01$6.78
Agent time / task15.4 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