DeepSeek V3 vs Step 3.5 Flash
DeepSeek V3 (2024) and Step 3.5 Flash (2026) are frontier reasoning models from DeepSeek and StepFun. DeepSeek V3 ships a 64k-token context window, while Step 3.5 Flash ships a 256K-token context window. On pricing, DeepSeek V3 costs $0.1/1M input tokens versus $0.1/1M 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.
Step 3.5 Flash fits 4x more tokens; pick it for long-context work and DeepSeek V3 for tighter calls.
Specs
| Released | 2024-12-26 | 2026-01-29 |
| Context window | 64k | 256K |
| Parameters | 671B | 196B (11B active) |
| Architecture | mixture of experts | mixture of experts |
| License | Open Source | Open Source |
| Knowledge cutoff | 2024-04 | - |
Pricing and availability
| DeepSeek V3 | Step 3.5 Flash | |
|---|---|---|
| Input price | $0.1/1M tokens | $0.1/1M tokens |
| Output price | $0.3/1M tokens | $0.3/1M tokens |
| Providers |
Capabilities
| DeepSeek V3 | Step 3.5 Flash | |
|---|---|---|
| Vision | ||
| Multimodal | ||
| Reasoning | ||
| Function calling | ||
| Tool use | ||
| Structured outputs | ||
| Code execution |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on reasoning mode: Step 3.5 Flash, function calling: DeepSeek V3, tool use: DeepSeek V3, and structured outputs: DeepSeek V3. 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 lists $0.1/1M input and $0.3/1M output tokens, while Step 3.5 Flash lists $0.1/1M input and $0.3/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts DeepSeek V3 lower by about $0 per million blended tokens. Availability is 12 providers versus 1, so concentration risk also matters.
Choose DeepSeek V3 when provider fit and broader provider choice are central to the workload. Choose Step 3.5 Flash when reasoning depth and larger context windows 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 or Step 3.5 Flash?
Step 3.5 Flash supports 256K tokens, while DeepSeek V3 supports 64k 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 or Step 3.5 Flash?
DeepSeek V3 is cheaper on tracked token pricing. DeepSeek V3 costs $0.1/1M input and $0.3/1M output tokens. Step 3.5 Flash costs $0.1/1M input and $0.3/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is DeepSeek V3 or Step 3.5 Flash open source?
DeepSeek V3 is listed under Open Source. Step 3.5 Flash is listed under Open Source. 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 or Step 3.5 Flash?
Step 3.5 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 or Step 3.5 Flash?
DeepSeek V3 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 and Step 3.5 Flash?
DeepSeek V3 is available on DeepInfra, Fireworks AI, DeepSeek Platform, Microsoft Foundry, and OpenRouter. Step 3.5 Flash is available on OpenRouter. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
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Last reviewed: 2026-04-24. Data sourced from public model cards and provider documentation.