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Claude Fable 5.1 vs DeepSeek V4 Flash (0731)

Claude Fable 5.1 is served by invitation. Its figures below are the live rates, but calls need a workspace grant first; ask us for access before you build on this comparison.

vs

Which one, when

Both share a 1,000,000-token context window, so the split is cost and modality: claude-fable-5-1 costs $10 per million input and $50 per million output, roughly 23x and 38x the $0.44 and $1.32 of deepseek-v4-flash-0731. Pick claude-fable-5-1 when you need image input alongside text or always-on thinking, which cannot be disabled on it. Pick deepseek-v4-flash-0731 for text-only chat, code, tools and reasoning at high volume, or when a single reply must run long - its 393216-token max output is about 3x the 128000 tokens allowed on claude-fable-5-1.

Benchmarks

Above averageNo peer higherClaude Fable 5.17 / 77 / 7DeepSeek V4 Flash (0731)4 / 110 / 11
Claude Fable 5.1 DeepSeek V4 Flash (0731) other models measured peer average no peer scored higher
Terminal-Bench 2.1
N/A
82.7%
OSWorld 2.0 partial
77.9%
N/A
Cybergym
N/A
76.7%
GDPval-AA v2 Elo · 1711-1853 per Anthropic · 2026-09-05
no peer scored higher 1853
N/A
Humanity's Last Exam no tools
no peer scored higher 60.9%
37.8%
Agents' Last Exam
N/A
25.2%

Vendor-published: Alibaba (Qwen) Anthropic DeepSeek Google MiniMax Moonshot OpenAI Tencent Z.ai

Pricing

Claude Fable 5.1 DeepSeek V4 Flash (0731) Δ
Input / 1M tokens $10 $0.44 23×
Output / 1M tokens $50 $1.32 38×
Cache read / 1M tokens $0.25 $0.044 5.7×
Cache write 1.25x (5m) / 2x (1h) no separate charge -

Rates from the live catalog at build time; each model page carries the current card.

Where they sit - input price per 1M tokens across all 67 chat models on this billing unit (log scale)

Capabilities

Claude Fable 5.1 DeepSeek V4 Flash (0731)
Tool use yes yes
Thinking control always on yes - vendor dial not published
Structured output yes yes
Prompt caching explicit (you mark the prefix) implicit (automatic)
Cache lifetime 5m default, 1h option no fixed TTL (evicted when unused)
Minimum cached prefix 1024 tokens not published

Specs

Claude Fable 5.1 DeepSeek V4 Flash (0731)
Input modalities text image text
Output modalities text text
Released 2026-09-01 2026-07-31
Knowledge cutoff 2026-06 -
Context window 1M 1M
Max output 128K 393K
Thinking parameter output_config.effort (thinking is adaptive-only and always on) -
Accepted values
effort
  • low
  • medium
  • high
  • xhigh
  • max
-
Default

thinking always on (adaptive)

effort
  • high
-

Specs are transcribed from each vendor’s documentation; a row a vendor does not publish is left out rather than inferred. Full sources: Claude Fable 5.1 · DeepSeek V4 Flash (0731)

Switch between them with one line

Both ids are in every tab below - the highlighted pair of lines is the only edit. Same endpoint, same key, same request shape.

from openai import OpenAI

client = OpenAI(
    base_url="https://synthorai.io/v1",
    api_key="sk-syn-...",
)

resp = client.chat.completions.create(
    model="claude-fable-5-1",
    # model="deepseek-v4-flash-0731",  # uncomment this line, comment the one above
    messages=[{"role": "user", "content": "Summarize this diff"}],
    reasoning_effort="medium",
)
print(resp.choices[0].message.content)

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FAQ

Which is cheaper, Claude Fable 5.1 or DeepSeek V4 Flash (0731)?

DeepSeek V4 Flash (0731) is cheaper on input / 1m tokens ($0.44 vs $10, 23× apart). Other rows may point the other way - the table above carries the full card, and real cost depends on your mix.

Can I A/B test Claude Fable 5.1 against DeepSeek V4 Flash (0731) without two integrations?

Yes. Both are served through the same OpenAI-compatible endpoint with one API key - switching is a one-line model-string change, so you can route a fraction of traffic to each and compare bills directly.

Do Claude Fable 5.1 and DeepSeek V4 Flash (0731) support prompt caching?

Yes - both bill cached reads below their input rate, so warm-prefix workloads cost less than the list rates suggest. The exact cache-read rows are in the pricing table above.

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