DeepSeek V3.1 Terminus vs Mistral Magistral Small 2509
DeepSeek V3.1 Terminus (2025) and Mistral Magistral Small 2509 (2025) are general-purpose language models from DeepSeek and MistralAI. DeepSeek V3.1 Terminus ships a 164K-token context window, while Mistral Magistral Small 2509 ships a not-yet-sourced context window. On pricing, DeepSeek V3.1 Terminus costs $0.21/1M input tokens versus $0.5/1M for the alternative. This comparison covers specs, pricing, capabilities, benchmarks, provider availability, and production fit.
DeepSeek V3.1 Terminus is ~138% cheaper at $0.21/1M; pay for Mistral Magistral Small 2509 only for provider fit.
Decision scorecard
Local evidence first| Signal | DeepSeek V3.1 Terminus | Mistral Magistral Small 2509 |
|---|---|---|
| Decision fit | RAG, Long context, and Classification | General |
| Context window | 164K | — |
| Cheapest output | $0.79/1M tokens | $1.5/1M tokens |
| Provider routes | 2 tracked | 1 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- DeepSeek V3.1 Terminus has the larger context window for long prompts, retrieval packs, or transcript analysis.
- DeepSeek V3.1 Terminus has the lower cheapest tracked output price at $0.79/1M tokens.
- DeepSeek V3.1 Terminus has broader tracked provider coverage for fallback and procurement flexibility.
- DeepSeek V3.1 Terminus uniquely exposes Structured outputs in local model data.
- Local decision data tags DeepSeek V3.1 Terminus for RAG, Long context, and Classification.
- Use Mistral Magistral Small 2509 when your own prompt tests beat the comparison signals; the local data does not show a decisive standalone advantage yet.
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
Mistral Magistral Small 2509
$775
Cheapest tracked route: AWS Bedrock
Estimated monthly gap: $410. Batch, cache, and negotiated pricing are excluded from this local estimate.
Switch friction
- No overlapping tracked provider route is sourced for DeepSeek V3.1 Terminus and Mistral Magistral Small 2509; plan for SDK, billing, or endpoint changes.
- Mistral Magistral Small 2509 is $0.71/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- Check replacement coverage for Structured outputs before moving production traffic.
- No overlapping tracked provider route is sourced for Mistral Magistral Small 2509 and DeepSeek V3.1 Terminus; plan for SDK, billing, or endpoint changes.
- DeepSeek V3.1 Terminus is $0.71/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- DeepSeek V3.1 Terminus adds Structured outputs in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2025-04-01 | 2025-09-01 |
| Context window | 164K | — |
| Parameters | — | — |
| Architecture | decoder only | - |
| License | Open Source | Proprietary |
| Knowledge cutoff | - | - |
Pricing and availability
| Pricing attribute | DeepSeek V3.1 Terminus | Mistral Magistral Small 2509 |
|---|---|---|
| Input price | $0.21/1M tokens | $0.5/1M tokens |
| Output price | $0.79/1M tokens | $1.5/1M tokens |
| Providers |
Capabilities
| Capability | DeepSeek V3.1 Terminus | Mistral Magistral Small 2509 |
|---|---|---|
| Vision | No | No |
| Multimodal | No | No |
| Reasoning | No | No |
| Function calling | No | No |
| Tool use | No | No |
| Structured outputs | Yes | No |
| Code execution | No | No |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on structured outputs: DeepSeek V3.1 Terminus. Both models share the core language-model surface, 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 Mistral Magistral Small 2509 lists $0.5/1M input and $1.5/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts DeepSeek V3.1 Terminus lower by about $0.42 per million blended tokens. Availability is 2 providers versus 1, so concentration risk also matters.
Choose DeepSeek V3.1 Terminus when provider fit, lower input-token cost, and broader provider choice are central to the workload. Choose Mistral Magistral Small 2509 when provider fit 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 is cheaper, DeepSeek V3.1 Terminus or Mistral Magistral Small 2509?
DeepSeek V3.1 Terminus is cheaper on tracked token pricing. DeepSeek V3.1 Terminus costs $0.21/1M input and $0.79/1M output tokens. Mistral Magistral Small 2509 costs $0.5/1M input and $1.5/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is DeepSeek V3.1 Terminus or Mistral Magistral Small 2509 open source?
DeepSeek V3.1 Terminus is listed under Open Source. Mistral Magistral Small 2509 is listed under Proprietary. 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 structured outputs, DeepSeek V3.1 Terminus or Mistral Magistral Small 2509?
DeepSeek V3.1 Terminus has the clearer documented structured outputs signal in this comparison. If structured outputs 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 Mistral Magistral Small 2509?
DeepSeek V3.1 Terminus is available on NVIDIA NIM and OpenRouter. Mistral Magistral Small 2509 is available on AWS Bedrock. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
When should I pick DeepSeek V3.1 Terminus over Mistral Magistral Small 2509?
DeepSeek V3.1 Terminus is ~138% cheaper at $0.21/1M; pay for Mistral Magistral Small 2509 only for provider fit. If your workload also depends on provider fit, start with DeepSeek V3.1 Terminus; if it depends on provider fit, run the same evaluation with Mistral Magistral Small 2509.
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Last reviewed: 2026-05-11. Data sourced from public model cards and provider documentation.