DeepSeek V3.1 Terminus vs DeepSeek V4 Flash
DeepSeek V3.1 Terminus (2025) and DeepSeek V4 Flash (2026) are frontier reasoning models from DeepSeek. DeepSeek V3.1 Terminus ships a 164K-token context window, while DeepSeek V4 Flash ships a 1M-token context window. On pricing, DeepSeek V4 Flash costs $0.14/1M input tokens versus $0.21/1M for the alternative. This comparison covers specs, pricing, capabilities, benchmarks, provider availability, and production fit. It focuses on practical selection signals rather than broad model-family marketing.
DeepSeek V4 Flash is ~50% cheaper at $0.14/1M; pay for DeepSeek V3.1 Terminus only for provider fit.
Decision scorecard
Local evidence first| Signal | DeepSeek V3.1 Terminus | DeepSeek V4 Flash |
|---|---|---|
| Decision fit | RAG, Long context, and Classification | Coding, RAG, and Agents |
| Context window | 164K | 1M |
| Cheapest output | $0.79/1M tokens | $0.28/1M tokens |
| Provider routes | 2 tracked | 2 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- Local decision data tags DeepSeek V3.1 Terminus for RAG, Long context, and Classification.
- DeepSeek V4 Flash has the larger context window for long prompts, retrieval packs, or transcript analysis.
- DeepSeek V4 Flash has the lower cheapest tracked output price at $0.28/1M tokens.
- DeepSeek V4 Flash uniquely exposes Reasoning, Function calling, and Tool use in local model data.
- Local decision data tags DeepSeek V4 Flash for Coding, RAG, and Agents.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output prices on this page.
DeepSeek V3.1 Terminus
$366
Cheapest tracked route: OpenRouter
DeepSeek V4 Flash
$182
Cheapest tracked route: DeepSeek Platform
Estimated monthly gap: $184. Batch, cache, and negotiated pricing are excluded from this local estimate.
Switch friction
- Provider overlap exists on OpenRouter; start route-level A/B tests there.
- DeepSeek V4 Flash is $0.51/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- DeepSeek V4 Flash adds Reasoning, Function calling, and Tool use in local capability data.
- Provider overlap exists on OpenRouter; start route-level A/B tests there.
- DeepSeek V3.1 Terminus is $0.51/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- Check replacement coverage for Reasoning, Function calling, and Tool use before moving production traffic.
Specs
| Specification | ||
|---|---|---|
| Released | 2025-04-01 | 2026-04-24 |
| Context window | 164K | 1M |
| Parameters | — | 284B |
| Architecture | decoder only | mixture of experts |
| License | Open Source | MIT |
| Knowledge cutoff | - | - |
Pricing and availability
| Pricing attribute | DeepSeek V3.1 Terminus | DeepSeek V4 Flash |
|---|---|---|
| Input price | $0.21/1M tokens | $0.14/1M tokens |
| Output price | $0.79/1M tokens | $0.28/1M tokens |
| Providers |
Capabilities
| Capability | DeepSeek V3.1 Terminus | DeepSeek V4 Flash |
|---|---|---|
| Vision | No | No |
| Multimodal | No | No |
| Reasoning | No | Yes |
| Function calling | No | Yes |
| Tool use | No | Yes |
| Structured outputs | Yes | Yes |
| Code execution | No | No |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on reasoning mode: DeepSeek V4 Flash, function calling: DeepSeek V4 Flash, and tool use: DeepSeek V4 Flash. Both models share structured outputs, so the practical split is not just feature count. Use those differences to decide whether the page is about raw model quality, agentic coding support, multimodal ingestion, or predictable structured API behavior.
For cost, DeepSeek V3.1 Terminus lists $0.21/1M input and $0.79/1M output tokens, while DeepSeek V4 Flash lists $0.14/1M input and $0.28/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts DeepSeek V4 Flash lower by about $0.2 per million blended tokens. Availability is 2 providers versus 2, so concentration risk also matters.
Choose DeepSeek V3.1 Terminus when provider fit are central to the workload. Choose DeepSeek V4 Flash when reasoning depth, larger context windows, and lower input-token cost are more important. For production, rerun your own prompts through the exact provider, region, and tool stack you plan to ship. This keeps the decision grounded in measurable tradeoffs instead of brand-level assumptions. It also helps separate model capability from provider packaging, which can change cost and latency.
FAQ
Which has a larger context window, DeepSeek V3.1 Terminus or DeepSeek V4 Flash?
DeepSeek V4 Flash supports 1M tokens, while DeepSeek V3.1 Terminus supports 164K tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
Which is cheaper, DeepSeek V3.1 Terminus or DeepSeek V4 Flash?
DeepSeek V4 Flash is cheaper on tracked token pricing. DeepSeek V3.1 Terminus costs $0.21/1M input and $0.79/1M output tokens. DeepSeek V4 Flash costs $0.14/1M input and $0.28/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is DeepSeek V3.1 Terminus or DeepSeek V4 Flash open source?
DeepSeek V3.1 Terminus is listed under Open Source. DeepSeek V4 Flash is listed under MIT. License labels affect whether you can self-host, redistribute weights, or rely only on hosted APIs, so confirm the upstream license before deployment.
Which is better for reasoning mode, DeepSeek V3.1 Terminus or DeepSeek V4 Flash?
DeepSeek V4 Flash has the clearer documented reasoning mode signal in this comparison. If reasoning mode is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Which is better for function calling, DeepSeek V3.1 Terminus or DeepSeek V4 Flash?
DeepSeek V4 Flash has the clearer documented function calling signal in this comparison. If function calling is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Where can I run DeepSeek V3.1 Terminus and DeepSeek V4 Flash?
DeepSeek V3.1 Terminus is available on NVIDIA NIM and OpenRouter. DeepSeek V4 Flash is available on DeepSeek Platform and OpenRouter. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
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Last reviewed: 2026-05-14. Data sourced from public model cards and provider documentation.