Model comparison

Claude Opus 5.5 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 Opus 5.5

Frontier

DeepSeek

DeepSeek V4.1 Flash

Balanced · Open weights

AI model capability comparison
Specification	Claude Opus 5.5	DeepSeek V4.1 Flash
Provider
Provider	Anthropic	DeepSeek
Tier
Tier	Frontier	Balanced
Context window
Context window	1M	1M
Max output
Max output	128K	Winner: 384K
Input / 1M tokens
Input / 1M tokens	$4	Winner: $0.30
Output / 1M tokens
Output / 1M tokens	$20	Winner: $1.20
Weights
Weights	Closed	Open
Parameters
Parameters	Not disclosedUnverified	552B MoE (causal encoder-decoder; 8B active for input, 16B for output)
Reasoning levels
Reasoning levels	adaptive	low, high, max
Modalities
Modalities	text, image	text, image
License
License	Not disclosedUnverified	MIT
API model id
API model id	claude-opus-5-5	deepseek-flash
Released
Released	September 22, 2026	September 10, 2026
Artificial Analysis Intelligence Index [max] (2026-09-26)
Artificial Analysis Intelligence Index [max] (2026-09-26)	Winner: 57.6	39.5
Humanity's Last Exam [max] (2026-09-26)
Humanity's Last Exam [max] (2026-09-26)	61.4	Not verifiedUnverified
Terminal-Bench 4.0 [max] (2026-09-26)
Terminal-Bench 4.0 [max] (2026-09-26)	59.6	Not verifiedUnverified
Terminal-Bench 4.0 [xhigh] (2026-09-22)
Terminal-Bench 4.0 [xhigh] (2026-09-22)	66.4	Not verifiedUnverified
DeepSWE 1.1 [max] (2026-09-10)
DeepSWE 1.1 [max] (2026-09-10)	Not verifiedUnverified	74.2
Terminal-Bench 2.1 [max] (2026-09-10)
Terminal-Bench 2.1 [max] (2026-09-10)	Not verifiedUnverified	90.6
GPQA Diamond [max] (2026-09-10)
GPQA Diamond [max] (2026-09-10)	Not verifiedUnverified	90.9

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 Terminal-Bench 4.0 (independent AA run, part of Intelligence Index v4.3.2)
Agentic terminal work: long multi-step tasks executed in a sandboxed shell environment.
Comparable with caveatNOT comparable with Terminal-Bench 2.x or 3.0 — 4.0 uses a new, non-overlapping task set. Within 4.0, scores from different harnesses (tbench.ai agent entries vs Artificial Analysis runs) are not interchangeable.
2026-09-26
Artificial Analysis Humanity's Last Exam (independent, 2,158 text-only questions)
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.
2026-09-26
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.
2026-09-22
Anthropic — Claude Opus 5.5 announcement (vendor; conflicts with AA's independent 59.6 — harness difference preserved)
Agentic terminal work: long multi-step tasks executed in a sandboxed shell environment.
Comparable with caveatNOT comparable with Terminal-Bench 2.x or 3.0 — 4.0 uses a new, non-overlapping task set. Within 4.0, scores from different harnesses (tbench.ai agent entries vs Artificial Analysis runs) are not interchangeable.
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

Pricing tiers

Claude Opus 5.5: $4/$20 per MTok, no long-context surcharge. Cache reads $0.20; 5-minute cache writes $5, 1-hour writes $8. Batch $2/$10; Fast mode $8/$40. Batches API allows 300K output with the output-300k-2026-03-24 beta header. Knowledge cutoff Jun 2026; retirement not before 2027-09-22.

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.

FrontierRecord checked September 26, 2026

Claude Opus 5.5

Claude Opus 5.5 is Anthropic's default model for agentic coding and knowledge work — Anthropic says it performs near Fable 5.1 on most work at about 40% lower running cost than Opus 5, and it leads the Artificial Analysis Intelligence Index v4.3.2.

Best for

Complex agentic coding
Enterprise knowledge work
Default frontier model

Watch out

Breaking changes from Opus 5: adaptive thinking cannot be disabled (effort runs low to max, default medium) and forced tool use returns an error. Verbose at max effort, so cap output on cost-sensitive routes.

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 $20 for Claude Opus 5.5 — about 17×. 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.
1 shared named benchmark with differing scores — Measured on: Artificial Analysis Intelligence Index.
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.

Claude Opus 5.5: Anthropic — Claude Opus 5.5 (accessed 2026-09-26)
Claude Opus 5.5: Anthropic docs — Opus 5.5 overview (1M context, 128K output) (accessed 2026-09-26)
Claude Opus 5.5: Anthropic pricing (claude-opus-5-5 $4/$20, cache reads $0.20) (accessed 2026-09-26)
Claude Opus 5.5: Artificial Analysis — Intelligence Index v4.3.2 (Opus 5.5 #1) (accessed 2026-09-26)
DeepSeek V4.1 Flash: DeepSeek — V4.1-Flash release (2026-09-10) (accessed 2026-09-26)
DeepSeek V4.1 Flash: DeepSeek API pricing (deepseek-flash $0.30/$1.20 peak) (accessed 2026-09-26)
DeepSeek V4.1 Flash: Hugging Face — deepseek-ai/DeepSeek-V4.1-Flash (accessed 2026-09-26)

Related comparisons

Diving deeper on one model? Claude Opus 5.5 · DeepSeek V4.1 Flash

Common questions

Claude Opus 5.5 vs DeepSeek V4.1 Flash

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

Is Claude Opus 5.5 or DeepSeek V4.1 Flash cheaper for input?

DeepSeek V4.1 Flash is cheaper at $0.30 per million input tokens, against $4 for Claude Opus 5.5 — roughly 13× 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 Opus 5.5 has tiered pricing: $4/$20 per MTok, no long-context surcharge. Cache reads $0.20; 5-minute cache writes $5, 1-hour writes $8. Batch $2/$10; Fast mode $8/$40. Batches API allows 300K output with the output-300k-2026-03-24 beta header. Knowledge cutoff Jun 2026; retirement not before 2027-09-22. 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 Opus 5.5 or DeepSeek V4.1 Flash cheaper for output?

DeepSeek V4.1 Flash is cheaper at $1.20 per million output tokens, against $20 for Claude Opus 5.5 — roughly 17× 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 Opus 5.5 has tiered pricing: $4/$20 per MTok, no long-context surcharge. Cache reads $0.20; 5-minute cache writes $5, 1-hour writes $8. Batch $2/$10; Fast mode $8/$40. Batches API allows 300K output with the output-300k-2026-03-24 beta header. Knowledge cutoff Jun 2026; retirement not before 2027-09-22. 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 Opus 5.5 or DeepSeek V4.1 Flash?

Both accept about 1M tokens of context, so document length will not decide between them.

Do Claude Opus 5.5 and DeepSeek V4.1 Flash support the same reasoning levels?

Claude Opus 5.5 exposes adaptive, while DeepSeek V4.1 Flash exposes low, high, max.

Should I use Claude Opus 5.5 or DeepSeek V4.1 Flash?

Claude Opus 5.5 is the frontier tier and DeepSeek V4.1 Flash the balanced tier. The useful question is whether your hardest task actually fails on the cheaper one — most production volume such as classification, extraction and summarisation does not.

Can I self-host Claude Opus 5.5 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 Opus 5.5 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 $4 for Claude Opus 5.5 — a 13.3x difference at the headline tier.
Measured capability: Claude Opus 5.5 leads Artificial Analysis Intelligence Index 57.6 to 39.5 (measured 2026-09-26).
Deployment: DeepSeek V4.1 Flash publishes weights you can self-host; the other is API-only.
Positioning: Claude Opus 5.5 sits in the frontier tier, DeepSeek V4.1 Flash in the balanced tier — most production volume (classification, extraction, summarisation) does not need the pricier tier.

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