DeepSeek R1 Basic vs Step 3.5 Flash
DeepSeek R1 Basic (2025) and Step 3.5 Flash (2026) are frontier-tier reasoning models from DeepSeek and StepFun. DeepSeek R1 Basic ships a 160k-token context window, while Step 3.5 Flash ships a 256k-token context window. On pricing, Step 3.5 Flash costs $0.10/1M input tokens versus $0.56/1M for the alternative. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads.
Step 3.5 Flash is ~460% cheaper at $0.10/1M; pay for DeepSeek R1 Basic only for provider fit.
Decision scorecard
Local evidence first| Signal | DeepSeek R1 Basic | Step 3.5 Flash |
|---|---|---|
| Best for | reasoning-heavy apps | reasoning-heavy apps |
| Decision fit | Long context | Coding, Agents, and Long context |
| Context window | 160k | 256k |
| Cheapest output | $1.68/1M tokens | $0.30/1M tokens |
| Provider routes | 1 tracked | 1 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- Local decision data tags DeepSeek R1 Basic for Long context.
- Step 3.5 Flash has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Step 3.5 Flash has the lower cheapest tracked output price at $0.30/1M tokens.
- Local decision data tags Step 3.5 Flash for Coding, Agents, and Long context.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output route or tier on this page.
DeepSeek R1 Basic
$868
Cheapest tracked route/tier: Fireworks AI
Step 3.5 Flash
$155
Cheapest tracked route/tier: OpenRouter
Estimated monthly gap: $713. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.
Switch friction
- No overlapping tracked provider route is sourced for DeepSeek R1 Basic and Step 3.5 Flash; plan for SDK, billing, or endpoint changes.
- Step 3.5 Flash is $1.38/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- No overlapping tracked provider route is sourced for Step 3.5 Flash and DeepSeek R1 Basic; plan for SDK, billing, or endpoint changes.
- DeepSeek R1 Basic is $1.38/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
Specs
| Specification | ||
|---|---|---|
| Released | 2025-01-01 | 2026-01-29 |
| Context window | 160k | 256k |
| Parameters | 671B | 196B (11B active) |
| Architecture | decoder only | mixture of experts |
| License | MIT(OSI) | Proprietary |
| Openness | Open source | Proprietary |
| Commercial use | Commercial use allowed | Commercial use with conditions |
| Knowledge cutoff | - | - |
Pricing and availability
| Pricing attribute | DeepSeek R1 Basic | Step 3.5 Flash |
|---|---|---|
| Input price | $0.56/1M tokens | $0.10/1M tokens |
| Output price | $1.68/1M tokens | $0.30/1M tokens |
| Providers |
Capabilities
| Capability | DeepSeek R1 Basic | Step 3.5 Flash |
|---|---|---|
| Vision | No | No |
| Multimodal | No | No |
| Reasoning | Yes | Yes |
| Function calling | No | No |
| Tool use | No | No |
| Structured outputs | No | No |
| Code execution | No | No |
| IDE integration | No | No |
| Computer use | No | No |
| Parallel agents | No | No |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint is close: both models cover reasoning mode. That makes context budget, benchmark fit, and provider maturity more important than a simple checklist. If your application depends on one integration detail, verify it against the provider route you plan to use, not just the base model listing.
For cost, DeepSeek R1 Basic lists $0.56/1M input and $1.68/1M output tokens on the cheapest tracked provider, while Step 3.5 Flash lists $0.10/1M input and $0.30/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts Step 3.5 Flash lower by about $0.74 per million blended tokens. Availability is 1 providers versus 1, so concentration risk also matters.
Choose DeepSeek R1 Basic when provider fit are central to the workload. Choose Step 3.5 Flash when long-context analysis, 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 R1 Basic or Step 3.5 Flash?
Step 3.5 Flash supports 256k tokens, while DeepSeek R1 Basic supports 160k 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 R1 Basic or Step 3.5 Flash?
Step 3.5 Flash is cheaper on tracked token pricing. DeepSeek R1 Basic costs $0.56/1M input and $1.68/1M output tokens. Step 3.5 Flash costs $0.10/1M input and $0.30/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is DeepSeek R1 Basic or Step 3.5 Flash open source?
DeepSeek R1 Basic is listed under MIT. Step 3.5 Flash 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 reasoning mode, DeepSeek R1 Basic or Step 3.5 Flash?
Both DeepSeek R1 Basic and Step 3.5 Flash expose reasoning mode. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface.
Where can I run DeepSeek R1 Basic and Step 3.5 Flash?
DeepSeek R1 Basic is available on Fireworks AI. Step 3.5 Flash is available on OpenRouter. Provider coverage can affect latency, region availability, compliance posture, and fallback options. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
When should I pick DeepSeek R1 Basic over Step 3.5 Flash?
Step 3.5 Flash is ~460% cheaper at $0.10/1M; pay for DeepSeek R1 Basic only for provider fit. If your workload also depends on provider fit, start with DeepSeek R1 Basic; if it depends on long-context analysis, run the same evaluation with Step 3.5 Flash.
Continue comparing
Last reviewed: 2026-05-29. Data sourced from public model cards and provider documentation.