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DeepSeek V4.1 Flash max vs Opus 5 medium

No clear quality winner: Opus 5 medium won 12, DeepSeek V4.1 Flash max won 6, 6 tied; DeepSeek V4.1 Flash max leads on cost: 13.8× cheaper; Opus 5 medium leads on agent time: 2.1× faster.

24 tasksData from

Stet score

DeepSeek V4.1 Flash maxdeepseek-harness · max reasoningRank 10 of 15

46.995% range 36.5–57.2

Opus 5 mediummedium reasoningRank 4 of 15

63.795% range 53.3–73.616.8 points higher

A directional read: their 95% score ranges overlap.

Cost / task

DeepSeek V4.1 Flash max$0.4913.8× cheaperfrom 23/24 tasks
Opus 5 medium$6.78

Agent time / task

DeepSeek V4.1 Flash max49.3 min
Opus 5 medium23.2 min2.1× faster

Quality

Head-to-head matchups

DeepSeek V4.1 Flash max won6

Tied6

Opus 5 medium won12

Opus 5 medium’s win share 63%, 95% range 46–79%Ties are within judge noise.

Task by task

DeepSeek V4.1 Flash max solved 1 task that Opus 5 medium didn’t, and Opus 5 medium solved 3 that DeepSeek V4.1 Flash max didn’t. Both solved 11; neither solved 9.

DeepSeek V4.1 Flash max only 1

  • stet-commit-342d0ac0Equivalent to the merged fix

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
TaskDeepSeek V4.1 Flash 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-15439c21Passed testsPassed testsBoth
stet-66762b4cPassed testsPassed testsBoth
stet-commit-5d766ddePassed testsEquivalent to the merged fixBoth
stet-commit-f0caded9Passed testsPassed testsBoth
stet-43493c52Passed testsPassed testsBoth
stet-6f84e978FailedPassed testsOpus 5 medium only
stet-2450ca2dFailedPassed testsOpus 5 medium only
stet-commit-f8ae1177FailedFailedNeither
stet-commit-342d0ac0Equivalent to the merged fixFailedDeepSeek V4.1 Flash 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
MetricDeepSeek V4.1 Flash maxOpus 5 medium
Harnessdeepseek-harness—
Reasoning effortmaxmedium
Rank10 of 154 of 15
Stet score46.995% range 36.5–57.263.795% range 53.3–73.6
Solved12/2411 passed, 1 judged equivalent14/2412 passed, 2 judged equivalent
Cost / task$0.49from 23/24 tasks$6.78
Agent time / task49.3 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