Figures current as of September 14, 2026 — the DeepSeek side is vendor-reported
V4.1 Flash shipped September 10, 2026. Every benchmark number on this page comes from DeepSeek's own model card; third-party labs had not re-run the model when we last checked. Prices are taken from DeepSeek's official rate card (off-peak) and Anthropic's published pricing.
See our earlier DeepSeek V4 Pro comparisonDeepSeek V4.1 Flash vs Claude Fable 5.1 · September 2026
DeepSeek V4.1 Flash vs Claude Fable 5.1
A $0.15 off-peak open-weights MoE against a $10 closed flagship — the same 1M-token window, wildly different bills and proof standards.
TL;DR
DeepSeek V4.1 Flash lists at $0.15/$0.60 per million input/output tokens off-peak (2x in Beijing business hours) against Claude Fable 5.1's flat $10/$50 — a 67x input price gap as of September 14, 2026. V4.1 Flash is a 552B-parameter MIT open-weights model with 1M context and 384K max output; its agentic-coding benchmark wins are vendor-reported and still unverified. Fable 5.1's 87.7% SWE-bench Verified and Anthropic-published rates are the checked side of this pair.
Specs at a glance
DeepSeek rates are its published off-peak prices; peak windows (01:00-04:00 and 06:00-10:00 UTC, Mon-Fri) double them. Fable 5.1 rates are Anthropic list prices, flat 24/7.
| Spec | DeepSeek V4.1 Flash | Claude Fable 5.1 |
|---|---|---|
| Model ID | deepseek-flash | claude-fable-5-1-20260902 |
| Released | September 10, 2026 | September 2, 2026 |
| Input price (per M tokens) | $0.15 | $10.00 |
| Output price (per M tokens) | $0.60 | $50.00 |
| Peak-hour billing | 2x input & output at peak ($0.30 / $1.20) | Flat rates 24/7, any context length |
| Cache read (per M tokens) | $0.003 | $0.25 |
| Architecture | 552B MoE - 8B active prefill, 16B decode | Undisclosed (closed API) |
| Weights & license | MIT open weights (~510 GB FP8) | Proprietary; API and cloud only |
| Context window | 1M | 1M |
| Max output | 384K | 128K |
The input gap is 67x, the output gap 83x. DeepSeek's automatic prefix caching bills cache hits at $0.003/MTok with no write fee; Fable 5.1 reads cache at $0.25/MTok after a paid write ($12.50/MTok for 5 minutes). Self-hosting flips the table: V4.1 Flash's ~510 GB FP8 MIT checkpoint realistically needs an 8-GPU node, while Fable 5.1 has no open weights at all.
Benchmarks - vendor numbers vs verified ones
DeepSeek published V4.1 Flash beating its own V4 Pro on agentic and coding suites at launch. Fable 5.1's strongest public coding score is Anthropic's 87.7% SWE-bench Verified. The only same-generation overlap is Terminal-Bench 4.0, run in different harnesses.
| Spec | DeepSeek V4.1 Flash | Claude Fable 5.1 |
|---|---|---|
| SWE-bench Verified | Not confirmed | 87.7% |
| DeepSWE v1.1 | 74.2% | Not confirmed |
| Terminal-Bench 2.1 | 90.6% | Not confirmed |
| Terminal-Bench 4.0 | 31.2% | 55.8% |
| GPQA Diamond | 90.9% | Not confirmed |
| HLE (no tools) | 36.8% | Not confirmed |
Sources: DeepSWE, Terminal-Bench 2.1, GPQA Diamond and HLE figures are DeepSeek's own model-card runs at maximum reasoning effort (September 10, 2026) - no independent replication yet. The Terminal-Bench 4.0 row mixes harnesses: 31.2% is DeepSeek's run, 55.8% comes from OpenAI's cross-model runs published with GPT-6 Astra. SWE-bench Verified is Anthropic-published; DeepSeek has not reported it. Treat vendor-vs-vendor gaps as indicative, not settled.
How to decide
Same 1M window, wildly different price and proof standards. Route by workload.
You run high-volume agents and the bill is the constraint
At $0.15/$0.60 off-peak, V4.1 Flash serves agentic loops for a fraction of flagship cost - and all weekend traffic plus most US daytime traffic bills off-peak. If your ceiling is API spend, not capability, that math is hard to argue with.
You need coding results that third parties can check
Fable 5.1 carries a published 87.7% SWE-bench Verified plus Artificial Analysis coverage; V4.1 Flash's DeepSWE 74.2 and Terminal-Bench 2.1 90.6 are DeepSeek's own harness runs, with no independent re-test as of September 14. If your team's eval needs externally reproduced numbers, the checked side is Fable 5.1.
You need weights you can run offline
MIT-licensed ~510 GB FP8 checkpoints with day-one vLLM and SGLang support put full ownership on the table - for an 8-GPU node, not a hobby rig. Fable 5.1 is closed: hosted API, Bedrock, Vertex AI and Microsoft Foundry only.
Your work is knowledge-heavy reasoning without tools
Even DeepSeek's own table shows the limit: HLE 36.8 against V4 Pro's 42.7 - V4.1 Flash is a Flash-class reasoner priced fast, not a frontier knowledge model. For long-form reasoning with no retrieval or tool scaffolding, Fable 5.1 stays the safer default.
Your prompts mostly repeat themselves
Stable system prompts and re-ingested documents hit the cache line, not the input line: $0.003/MTok on V4.1 Flash (off-peak, no write fee) against $0.25/MTok on Fable 5.1 (after a paid write). Both crush their own uncached price - see our Fable 5.1 prompt-caching breakdown for the Anthropic side.
The honest summary: V4.1 Flash buys you 67x-cheaper input and real open-weights ownership, at the price of vendor-only benchmarks, peak-window billing and a knowledge-reasoning ceiling. Fable 5.1 buys you verified coding depth and flat-rate 1M context. The right answer changes the moment Artificial Analysis publishes V4.1 Flash numbers - we will update this page when they land.
Price out your own workload
Cache hit rates, peak-hour routing and output length move this comparison more than the headline rates. Model your token mix against the current rate card.