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DeepSeek V4.1 Flash max vs Haiku 5.5 max

No clear quality winner: Haiku 5.5 max won 12, DeepSeek V4.1 Flash max won 5, 6 tied, 1 undecided; DeepSeek V4.1 Flash max leads on cost and agent time: 7.8× cheaper and 1.2× faster.

24 tasksData from

Stet score

DeepSeek V4.1 Flash maxdeepseek-harness · max reasoningRank 11 of 16

45.995% range 35.5–56.1

Haiku 5.5 maxclaude-code · max reasoningRank 8 of 16

55.595% range 44.6–65.79.6 points higher

A directional read: their 95% score ranges overlap.

Cost / task

DeepSeek V4.1 Flash max$0.497.8× cheaperfrom 23/24 tasks
Haiku 5.5 max$3.85

Agent time / task

DeepSeek V4.1 Flash max49.3 min1.2× faster
Haiku 5.5 max58.4 min

Quality

Head-to-head matchups

DeepSeek V4.1 Flash max won5

Tied61 undecided

Haiku 5.5 max won12

Haiku 5.5 max’s win share 63%, 95% range 47–79%Ties are within judge noise.

Task by task

DeepSeek V4.1 Flash max solved 3 tasks that Haiku 5.5 max didn’t, and Haiku 5.5 max solved 3 that DeepSeek V4.1 Flash max didn’t. Both solved 9; neither solved 8.

DeepSeek V4.1 Flash max only 3

  • stet-232b50baPassed tests
  • stet-66762b4cPassed tests
  • stet-43493c52Passed tests

Haiku 5.5 max only 3

  • stet-6f84e978Equivalent to the merged fix
  • stet-2450ca2dPassed tests
  • stet-commit-f8ae1177Passed tests

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. 1 of the 24 tasks is left out because one of the two has no scored result on it.

All 23 compared tasks
Task by task
TaskDeepSeek V4.1 Flash maxHaiku 5.5 maxSolved by
stet-3169aefaPassed testsPassed testsBoth
stet-89dfbc27Passed testsPassed testsBoth
stet-b28f4fe7Passed testsPassed testsBoth
stet-232b50baPassed testsFailedDeepSeek V4.1 Flash max only
stet-5276aa3fPassed testsPassed testsBoth
stet-commit-bbbbae09Passed testsPassed testsBoth
stet-66762b4cPassed testsFailedDeepSeek V4.1 Flash max only
stet-15439c21Passed testsPassed testsBoth
stet-commit-5d766ddePassed testsEquivalent to the merged fixBoth
stet-43493c52Passed testsFailedDeepSeek V4.1 Flash max only
stet-commit-f0caded9Passed testsPassed testsBoth
stet-6f84e978FailedEquivalent to the merged fixHaiku 5.5 max only
stet-2450ca2dFailedPassed testsHaiku 5.5 max only
stet-commit-342d0ac0Equivalent to the merged fixEquivalent to the merged fixBoth
stet-commit-f8ae1177FailedPassed testsHaiku 5.5 max only
stet-commit-5e075641FailedFailedNeither
stet-commit-2826765eFailedFailedNeither
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 maxHaiku 5.5 max
Harnessdeepseek-harnessclaude-code
Reasoning effortmaxmax
Rank11 of 168 of 16
Stet score45.995% range 35.5–56.155.595% range 44.6–65.7
Solved12/2411 passed, 1 judged equivalent12/249 passed, 3 judged equivalent
Cost / task$0.49from 23/24 tasks$3.85
Agent time / task49.3 min58.4 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