Claude Opus 5.5 (max) vs DeepSeek V4.1 Flash (max)

Head-to-head on the Towards AI writing benchmark: same 10 real YouTube scripts, five runs each, scored blind by a three-family judge panel. Claude Opus 5.5 (max) leads overall, 91.8 to 88.1.

Claude Opus 5.5 (max)

#1 Elo 2846 · 91.8/100

DeepSeek V4.1 Flash (max)

#28 Elo 2183 · 88.1/100

Cost / script

$3.433 vs $0.013

Human baseline

90.9 Claude Opus 5.5 (max) exceeds it · DeepSeek V4.1 Flash (max) falls below it

The verdict

Claude Opus 5.5 (max effort) wins this one, and the board is not close: #1 at 2845.8 Elo and 91.77 overall, against #28, 2183.1 Elo and 88.11 overall for DeepSeek V4.1 Flash (max). The 95% Elo intervals do not overlap (2790.8 to 2899.6 against 2147.5 to 2214.6). Where Claude Opus 5.5 (max effort) pulls ahead: Length Adherence (97.62 vs 91.98) and Visual Cue Quality (89.31 vs 84.51). DeepSeek V4.1 Flash (max) does not take a single metric off Claude Opus 5.5 (max effort) in this pairing. The trade is price: DeepSeek V4.1 Flash (max) costs about $0.013 per article against $3.433 for Claude Opus 5.5 (max effort), so you pay for the higher rank. DeepSeek V4.1 Flash (max) publishes open weights; Claude Opus 5.5 (max effort) does not. Default to Claude Opus 5.5 (max effort). Reach for DeepSeek V4.1 Flash (max) when the lower price and open weights matter more to you than the headline rank.

Pick Claude Opus 5.5 (max effort) for the stronger board result, length adherence, and visual cues.
Pick DeepSeek V4.1 Flash (max) for the lower price and open weights.

Reading the Elo intervals. Each range estimates uncertainty around one model's Elo. We repeatedly sample from every model's recorded run scores on each task and recalculate the full ranking. Comparing these separate ranges does not test the Elo gap between two models. The tasks stay fixed, so the ranges do not measure how the ranking would change on new tasks.

Metric by metric

Blue bars: Claude Opus 5.5 (max). Orange bars: DeepSeek V4.1 Flash (max). Same 0–100 scale; the bold bar wins that metric.

Tone & Voice Match19% weight

91.0

88.0

Writing Craft & Clarity13% weight

91.5

88.8

Substance, Accuracy & Value15% weight

90.7

86.8

Continuity & Emotion14% weight

90.9

86.9

YouTube Best Practices12% weight

91.7

87.8

Hook Strength10% weight

91.2

88.3

Length Adherence8% weight

97.6

92.0

Slop Score (EQ-Bench + ours)5% weight

94.9

91.3

Visual Cue Quality4% weight

89.3

84.5

Everything else that differs

	Claude Opus 5.5 (max)	DeepSeek V4.1 Flash (max)
Overall / 100	91.8	88.1
Writing Elo	2846	2183
Run-to-run spread (± overall std)	0.850	1.120
Cost per script (USD)	3.433	0.013
Avg latency (s)	1,023.3	76.2
Open weights	No	Yes

Full scorecards: Claude Opus 5.5 (max) · DeepSeek V4.1 Flash (max). How scoring works: methodology.

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