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Model comparison

Claude Sonnet 5 vs DeepSeek V4.1 Flash

Anthropic against DeepSeek, compared on context, price, and verified benchmark results.

Catalog record checked September 26, 2026Individual provider fields may changeEvidence confidence: High — see receipts below

Anthropic

Claude Sonnet 5

Balanced

vs

DeepSeek

DeepSeek V4.1 Flash

Balanced · Open weights

AI model capability comparison
SpecificationClaude Sonnet 5DeepSeek V4.1 Flash
ProviderAnthropicDeepSeek
TierBalancedBalanced
Context window1M1M
Max output128KWinner: 384K
Input / 1M tokens$2Winner: $0.30
Output / 1M tokens$10Winner: $1.20
WeightsClosedOpen
ParametersNot disclosedUnverified552B MoE (causal encoder-decoder; 8B active for input, 16B for output)
Reasoning levelsadaptivelow, high, max
Modalitiestext, imagetext, image
LicenseNot disclosedUnverifiedMIT
API model idclaude-sonnet-5deepseek-flash
ReleasedJune 30, 2026September 10, 2026
Artificial Analysis Intelligence Index [max] (2026-09-26)38.2Winner: 39.5
Terminal-Bench 2.1 (2026-06-30)80.4Not verifiedUnverified
Terminal-Bench 2.1 [max] (2026-09-10)Not verifiedUnverified90.6
Humanity's Last Exam (2026-06-30)57.4Not verifiedUnverified
SWE-bench Verified (2026-09-01)79.6Not verifiedUnverified
LiveBench (2026-09-05)76Not verifiedUnverified
DeepSWE 1.1 [max] (2026-09-10)Not verifiedUnverified74.2
GPQA Diamond [max] (2026-09-10)Not verifiedUnverified90.9

Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Bold indicates the better figure where one is objectively better. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.

Benchmark receipts

Where each score comes from, and how far it can be compared across models.

  • 2026-09-26
    Artificial Analysis

    Composite index blending reasoning, knowledge, and coding evals into one 0–100 score.

    Comparable with caveatOnly same-version scores are comparable. v4.3.2 was rebaselined (the top score fell from 66 on v4.1.1 to ~58), so v4.1.1 figures must not be compared with v4.3.2 figures — check measuredAt.

  • 2026-09-10
    DeepSeek V4.1-Flash release notes (vendor)

    Agentic software engineering: pass@1 on real repo tasks with reported cost per completed task.

    Directly comparable

  • 2026-09-05
    LiveBench official leaderboard (benchmark-owned), xhigh effort

    Contamination-resistant general capability across reasoning, coding, math, data analysis, and language, with monthly question refreshes.

    Comparable with caveatRolling question set: observations months apart measure different question mixes. Record the measurement date and compare within ~1 month windows.

  • 2026-09-01
    vals.ai SWE-bench Verified leaderboard (independent, mini-swe-agent bash-only); not published by Anthropic; a 72.7 CosmicJS claim is unverified

    Real GitHub issue resolution: does the model's patch pass the hidden tests.

    Comparable with caveatPost-audit vendor claims and pre-audit scores sit on different task trust levels; scaffolding (agent harness, compute budget) also dominates results. Never aggregate across scaffolds.

  • 2026-06-30
    Anthropic announcement (vendor, with tools)

    Frontier-knowledge ceiling: extremely hard multi-domain questions written to be near-impossible without deep expertise.

    Comparable with caveatSubset/tool configurations (text-only vs with-tools) differ between vendors and materially change scores; must match configuration to compare.

  • 2026-06-30
    Anthropic announcement table (vendor, default effort; via Vellum transcription)

    Agentic terminal work: multi-step tasks executed in a sandboxed shell environment.

    Comparable with caveatNot comparable with Terminal-Bench 3.0 or 4.0 (different task sets) or v1; harness configuration (container, time limits) also shifts results.

Pricing tiers

Claude Sonnet 5: Standard $2/$10 per MTok; cache reads 10% of base input. Knowledge cutoff Jan 2026.

DeepSeek V4.1 Flash: Official peak rates $0.30/$1.20 per MTok; off-peak $0.15/$0.60 (50% of peak). Cache hit $0.006 peak / $0.003 off-peak. Peak hours are weekdays 01:00–04:00 and 06:00–10:00 UTC. Open weights (MIT). The legacy deepseek-v4-flash and deepseek-v4-flash-vision-exp ids temporarily route here.

BalancedRecord checked September 26, 2026

Claude Sonnet 5

Claude Sonnet 5 is Anthropic's best speed/intelligence balance for high-volume agentic work at $2/$10.

Best for

  • Everyday generation
  • High-volume agents
  • Cost-sensitive work

Watch out

A step below Opus 5.5 on the hardest tasks; pick Opus 5.5 when quality is paramount. Sonnet 5.5 is announced but not yet released.

BalancedOpen weightsRecord checked September 26, 2026

DeepSeek V4.1 Flash

DeepSeek V4.1 Flash is DeepSeek's new default — an open-weight (MIT) multimodal MoE that DeepSeek says beats V4-Pro on performance, cost and speed.

Best for

  • Open-weight price-performance
  • High-volume hosted agents
  • Self-hosting with MIT weights

Watch out

Vendor benchmark claims are far ahead of its independent Artificial Analysis score (39.5 on v4.3.2); peak/off-peak billing means the hour you run matters.

When the cheaper one wins

DeepSeek V4.1 Flash is cheaper on output at $1.20 per million tokens against $10 for Claude Sonnet 5 — about 8.3×. Use the cheaper tier for classification, extraction, summarisation, and any task where the expensive model’s extra score does not change the accepted output. The expensive one only pays if your hardest task actually fails on the cheap tier. These are standard-tier API rates, excluding batch and cache discounts.

Run the model picker

Evidence confidence: High

How strong and complete the evidence behind this comparison is — not a prediction of which model is better.

  • Pricing verified on both sides — Input and output rates are verified for both models.
  • 4/5 core specs verified on both sides — Not published for at least one side: parameter count.
  • 2 shared named benchmarks with differing scores — Measured on: Artificial Analysis Intelligence Index, Terminal-Bench 2.1.
  • Verified within the last 90 days — Newest catalog check was 2 days ago.
  • Both models carry source citations — Each side has at least two catalog sources on record.

Source receipts

Each catalog figure was checked against the provider or an independent second source on the date shown.

Related comparisons

Diving deeper on one model? Claude Sonnet 5 · DeepSeek V4.1 Flash

Common questions

Claude Sonnet 5 vs DeepSeek V4.1 Flash

Answered from the verified figures on this page rather than general guidance.

Is Claude Sonnet 5 or DeepSeek V4.1 Flash cheaper for input?
DeepSeek V4.1 Flash is cheaper at $0.30 per million input tokens, against $2 for Claude Sonnet 5 — roughly 6.7× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Sonnet 5 has tiered pricing: Standard $2/$10 per MTok; cache reads 10% of base input. Knowledge cutoff Jan 2026. DeepSeek V4.1 Flash has tiered pricing: Official peak rates $0.30/$1.20 per MTok; off-peak $0.15/$0.60 (50% of peak). Cache hit $0.006 peak / $0.003 off-peak. Peak hours are weekdays 01:00–04:00 and 06:00–10:00 UTC. Open weights (MIT). The legacy deepseek-v4-flash and deepseek-v4-flash-vision-exp ids temporarily route here.
Is Claude Sonnet 5 or DeepSeek V4.1 Flash cheaper for output?
DeepSeek V4.1 Flash is cheaper at $1.20 per million output tokens, against $10 for Claude Sonnet 5 — roughly 8.3× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Sonnet 5 has tiered pricing: Standard $2/$10 per MTok; cache reads 10% of base input. Knowledge cutoff Jan 2026. DeepSeek V4.1 Flash has tiered pricing: Official peak rates $0.30/$1.20 per MTok; off-peak $0.15/$0.60 (50% of peak). Cache hit $0.006 peak / $0.003 off-peak. Peak hours are weekdays 01:00–04:00 and 06:00–10:00 UTC. Open weights (MIT). The legacy deepseek-v4-flash and deepseek-v4-flash-vision-exp ids temporarily route here.
Which has the larger context window, Claude Sonnet 5 or DeepSeek V4.1 Flash?
Both accept about 1M tokens of context, so document length will not decide between them.
Do Claude Sonnet 5 and DeepSeek V4.1 Flash support the same reasoning levels?
Claude Sonnet 5 exposes adaptive, while DeepSeek V4.1 Flash exposes low, high, max.
Should I use Claude Sonnet 5 or DeepSeek V4.1 Flash?
Both sit in the balanced tier, so the choice usually comes down to price and context rather than capability. Claude Sonnet 5 suits everyday generation; DeepSeek V4.1 Flash suits open-weight price-performance.
Can I self-host Claude Sonnet 5 or DeepSeek V4.1 Flash?
DeepSeek V4.1 Flash publishes open weights, but self-hosting and third-party provider access depend on the licence, hardware, serving support, and availability. Claude Sonnet 5 is a closed model whose supported access paths are controlled by its provider.

Next step

Choosing between them

The verified figures that separate this pair, computed from the catalog rather than restated boilerplate.

  • Input price: DeepSeek V4.1 Flash costs $0.30 per 1M tokens versus $2 for Claude Sonnet 5 — a 6.7x difference at the headline tier.
  • Measured capability: DeepSeek V4.1 Flash leads Artificial Analysis Intelligence Index 39.5 to 38.2 (measured 2026-09-26).
  • Deployment: DeepSeek V4.1 Flash publishes weights you can self-host; the other is API-only.
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