GLM 5.3 Flash high vs GPT 6 Luna low

No clear quality winner: GLM 5.3 Flash high won 12, GPT 6 Luna low won 4, 7 tied, 1 undecided; GPT 6 Luna low leads on cost and agent time: 7.7× cheaper and 3.9× faster.

24 tasksData from October 29, 2026

Stet score

GLM 5.3 Flash highcodex · high reasoningRank 15 of 16

29.095% range 19.9–39.39.1 points higher

GPT 6 Luna lowcodex · low reasoningRank 16 of 16

19.995% range 11.6–29.5

Other setups

Muse Wonder Full low

70.4

GPT 5.6 Luna max

70.3

SWE-2 Max high

64.3

GPT 6.1 Sol medium

62.5

Opus 5 medium

62.3

Grok 4.7 high

60.7

Pareto 26.9 medium

57.1

Haiku 5.5 max

55.5

GPT 6 Sol medium

55.4

GPT 6 Luna max

47.4

DeepSeek V4.1 Flash max

45.9

Opus 4.8 medium

39.2

Haiku 5.5 low

38.9

Muse Spark 1.3 high

31.9

A directional read: their 95% score ranges overlap.

Cost / task

GLM 5.3 Flash high$0.41

GPT 6 Luna low$0.057.7× cheaper

Agent time / task

GLM 5.3 Flash high26.7 min

GPT 6 Luna low6.9 min3.9× faster

Quality

Head-to-head matchups

GLM 5.3 Flash high won12

Tied71 undecided

GPT 6 Luna low won4

GLM 5.3 Flash high’s win share 69%, 95% range 53–84%Ties are within judge noise.

Task by task

GLM 5.3 Flash high solved 4 tasks that GPT 6 Luna low didn’t, and GPT 6 Luna low solved 0 that GLM 5.3 Flash high didn’t. Both solved 5; neither solved 14.

GLM 5.3 Flash high only 4

stet-5276aa3fPassed tests
stet-commit-bbbbae09Passed tests
stet-66762b4cPassed tests
stet-commit-f0caded9Passed tests

GPT 6 Luna low only 0

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
Task	GLM 5.3 Flash high	GPT 6 Luna low	Solved by
`stet-3169aefa`	Passed tests	Passed tests	Both
`stet-89dfbc27`	Passed tests	Passed tests	Both
`stet-b28f4fe7`	Passed tests	Passed tests	Both
`stet-232b50ba`	Passed tests	Passed tests	Both
`stet-5276aa3f`	Passed tests	Failed	GLM 5.3 Flash high only
`stet-commit-bbbbae09`	Passed tests	No change made	GLM 5.3 Flash high only
`stet-66762b4c`	Passed tests	Failed	GLM 5.3 Flash high only
`stet-15439c21`	Passed tests	Passed tests	Both
`stet-commit-5d766dde`	Failed	No change made	Neither
`stet-43493c52`	Failed	Failed	Neither
`stet-commit-f0caded9`	Passed tests	Failed	GLM 5.3 Flash high only
`stet-6f84e978`	Failed	Failed	Neither
`stet-2450ca2d`	Failed	Failed	Neither
`stet-commit-342d0ac0`	Failed	Failed	Neither
`stet-commit-f8ae1177`	Failed	No change made	Neither
`stet-commit-5e075641`	Failed	Failed	Neither
`stet-commit-2826765e`	Failed	Failed	Neither
`stet-commit-a8716b88`	Failed	Failed	Neither
`stet-commit-e928166f`	Failed	Failed	Neither
`stet-commit-30506f8e`	Failed	Failed	Neither
`stet-commit-87814583`	Failed	Failed	Neither
`stet-commit-d2ab0c25`	Failed	Failed	Neither
`stet-commit-e41c2e2d`	Failed	Failed	Neither

Side by side

Side by side
Metric	GLM 5.3 Flash high	GPT 6 Luna low
Harness	codex	codex
Reasoning effort	high	low
Rank	15 of 16	16 of 16
Stet score	29.095% range 19.9–39.3	19.995% range 11.6–29.5
Solved	9/249 passed, 0 judged equivalent	5/245 passed, 0 judged equivalent
Cost / task	$0.41	$0.05
Agent time / task	26.7 min	6.9 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 October 29, 2026.
Both setups come from the same leaderboard run of 16 setups: bmk_d4ba310fdf50db4ccb2092e3.

See all 16 setups on the leaderboard How Stet measures