Foreverse Research · Fiction Bench
How good is DeepSeek V4 Flash at writing fiction?
Depends on the book. On traditional xuanhuan fantasy it ranked #1 of nine in both blind packs — judges called it “the only one that reads like a real next chapter.” On formal court romance it slid to 6-7 of 9. It's also one of the cheapest models on the board.
Xuanhuan fantasy
1 / 9
Both packs: p303 #1 · p404 #1
Won all three windows; judges called it “the only system that gets better as it writes” — opens new arcs in the late window instead of flagging. High-confidence #1.
Court romance
6-7 / 9
Both packs: p505 #7 · p606 #6
The xuanhuan champion slid to lower-mid on court romance — its plain, fast-talking strengths don't transfer to formal period prose.
What the 20-round chains actually showed
Ranked #1 in both xuanhuan blind packs (p303/p404). Judges' sketch: “the only system that reads like a real next chapter” — dialogue-driven, colloquial address, standalone onomatopoeia, fast pacing, first in nearly every window; the nine-model round added “the only system that gets better as it writes.”
On the court-romance track (D2 directive) it slid to 6-7 of 9: the same plain, fast-talking pen stops sounding right in first-person limited, etiquette-heavy period prose. The two genre crowns going to different models is the series' single most important finding.
Structural metrics and blind judgment agree on this one: sentence-length CV recovered 0.56→0.64 late, zero marker echoes in 20 rounds. It's also the cost floor of the board — $0.14/M input at list price; ten thousand characters of new prose costs about three US cents (see cost-column note).
Long-run failure mode
None observed
None of the three long-run failure modes observed across the 20-round chain; zero marker echoes.
Structural fingerprint
Sentence-length CV 0.56→0.64 (gold 0.837); dialogue-driven, standalone onomatopoeia, fast pacing; zero marker echoes in 20 rounds.
Cross-genre profile: King of xuanhuan: plain speech, fast pacing and barked forms of address are its native register; formal literary prose is not.
Test-condition disclosure (hosted models are moving targets)
Model under test: deepseek-v4-flash (released 2026-07-31)
Evaluated: 2026-07-16 · Access channel: DeepSeek official API
Protocol: one 20-round continuous chain per genre · temperature 0.7 · double-blind full ranking with two shuffled mappings · structural-metric cross-checks
Directive condition: xuanhuan chains = legacy directive / romance chains = corrected D2 directive (full note in the leaderboard's method section)
What 10,000 characters cost
$0.032 list price: in $0.14/M · out $0.28/M (models.dev snapshot 2026-08-12)
Using the app's continuation recipe: one segment ≈ 400 chars = 8k input + 550 output tokens; 10k chars ≈ 25 segments; no cache discount. For between-model comparison only.
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How to cite
Foreverse Research, “How good is DeepSeek V4 Flash at writing fiction (Fiction Bench),” 2026-07. https://foreverse.app/research/fiction-bench/deepseek-v4-flash