DeepSeek V4 Flash vs GPT-5.5

Name: DeepSeek V4 Flash
Author: DeepSeek

DeepSeek V4 Flash (2026) and GPT-5.5 (2026) are frontier-tier reasoning models from DeepSeek and OpenAI. DeepSeek V4 Flash ships a 1m-token context window, while GPT-5.5 ships a 1.05m-token context window. On MMLU PRO, GPT-5.5 leads by 1.7 pts. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads.

DeepSeek V4 Flash is safer overall; choose GPT-5.5 when coding workflow support matters.

Decision scorecard

Local evidence first

Signal	DeepSeek V4 Flash	GPT-5.5	How to read it
Best for	reasoning-heavy apps, tool-calling agents, and long-context analysis	reasoning-heavy apps, multimodal apps, and tool-calling agents	Use-case synthesis from product type, capability flags, context, and provider data.
Decision fit	Coding, RAG, and Agents	Coding, RAG, and Agents	Primary workload tags from local decision data.
Context window	1m	1.05m	Higher is better when prompts, retrieval chunks, or transcripts are large.
Cheapest output	$0.12/1M tokens	$30/1M tokens	Cheapest tracked provider route; verify your exact region and tier.
Provider routes	5 tracked	4 tracked	Broader coverage can reduce vendor lock-in and fallback risk.
Shared benchmarks	12 shared	MMLU PRO leader	Visible benchmark lead is 1.7 points on MMLU PRO.

Decision tradeoffs

Choose DeepSeek V4 Flash when...

DeepSeek V4 Flash has the lower cheapest tracked output price at $0.12/1M tokens.
DeepSeek V4 Flash has broader tracked provider coverage for fallback and route flexibility.
Local decision data tags DeepSeek V4 Flash for Coding, RAG, and Agents.

Choose GPT-5.5 when...

GPT-5.5 holds a shared-benchmark lead on MMLU PRO, ahead by 1.7 points.
GPT-5.5 has the larger context window for long prompts, retrieval packs, or transcript analysis.
GPT-5.5 uniquely exposes Vision, Multimodal, and Code execution in local model data.
Local decision data tags GPT-5.5 for Coding, RAG, and Agents.

Monthly cost at traffic

Estimate token spend from the cheapest tracked input and output route or tier on this page.

Lower estimate DeepSeek V4 Flash

Requests / monthInput tokens / requestOutput tokens / request

DeepSeek V4 Flash

$76.26

Cheapest tracked route/tier: OpenRouter

GPT-5.5

$11,500

Cheapest tracked route/tier: OpenAI API 0-272K input tokens

Estimated monthly gap: $11,424. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.

Switch friction

DeepSeek V4 Flash -> GPT-5.5

Provider overlap exists on OpenRouter and Vercel AI Gateway; start route-level A/B tests there.
GPT-5.5 is $29.88/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
GPT-5.5 adds Vision, Multimodal, and Code execution in local capability data.

GPT-5.5 -> DeepSeek V4 Flash

Provider overlap exists on OpenRouter and Vercel AI Gateway; start route-level A/B tests there.
DeepSeek V4 Flash is $29.88/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
Check replacement coverage for Vision, Multimodal, and Code execution before moving production traffic.

Specs

Specification	DeepSeek V4 Flash DeepSeek	GPT-5.5 OpenAI
Released	2026-04-24	2026-04-23
Context window	1m	1.05m
Parameters	284B	—
Architecture	Mixture of Experts	Decoder Only
License	MITOSI-approved	Proprietary
Openness	Open source	Proprietary
Weights	Available	Not released
Code	Unknown	Unknown
Commercial use	Commercial use: permitted	Commercial use: conditional
Knowledge cutoff	-	2025-12

Pricing and availability

Pricing attribute	DeepSeek V4 Flash	GPT-5.5
Input price	Off-peak $0.22/1M tokens All UTC hours outside DeepSeek's peak windows. Cache-hit input: $0.007 per 1M tokens; cache-miss input: $0.22 per 1M; output: $0.66 per 1M. Peak $0.44/1M tokens 01:00-04:00 and 06:00-10:00 UTC. Cache-hit input: $0.014 per 1M tokens; cache-miss input: $0.44 per 1M; output: $1.32 per 1M.	0-272K input tokens $5/1M tokens Standard GPT-5.5 token pricing before the long-context surcharge threshold. 272K+ input tokens $8/1M tokens Long-context surcharge applies above 272K input tokens for the full session.
Output price	Off-peak $0.66/1M tokens All UTC hours outside DeepSeek's peak windows. Cache-hit input: $0.007 per 1M tokens; cache-miss input: $0.22 per 1M; output: $0.66 per 1M. Peak $1.32/1M tokens 01:00-04:00 and 06:00-10:00 UTC. Cache-hit input: $0.014 per 1M tokens; cache-miss input: $0.44 per 1M; output: $1.32 per 1M.	0-272K input tokens $30/1M tokens Standard GPT-5.5 token pricing before the long-context surcharge threshold. 272K+ input tokens $36/1M tokens Long-context surcharge applies above 272K input tokens for the full session.
Providers	DeepSeek Platform OpenRouter Microsoft Foundry Vercel AI Gateway Novita AI	OpenAI API OpenRouter Vercel AI Gateway AWS Bedrock

Capabilities

Capability	DeepSeek V4 Flash	GPT-5.5
Vision	No	Yes
Multimodal	No	Yes
Reasoning	Yes	Yes
JSON / Tool use	Yes	Yes
Structured outputs	Yes	Yes
Code execution	No	Yes
IDE integration	No	No
Computer use	No	No
Parallel agents	No	No

Benchmarks

Benchmark	DeepSeek V4 Flash	GPT-5.5
MMLU PRO	86.4	88.1
SWE-bench Verified	79.0	82.6
SWE-bench Pro	52.6	58.6
Google-Proof Q&A	88.1	93.6
Humanity's Last Exam	34.8	41.4
HumanEval	69.5	94.2
Chatbot Arena	1437.0	1488.0
Terminal-Bench 2.0	56.9	82.7
BrowseComp	73.2	84.4
GeneBench-Pro	2.4	12.0
MCP-Atlas	69.0	75.3
Massive Multitask Language Understanding	88.7	92.4

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Last reviewed: 2026-07-03. Data sourced from public model cards and provider documentation.

Both models

DeepSeek V4 Flash GPT-5.5