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 LiveCodeBench, Step 3.5 Flash leads by 36.8 pts. On pricing, both list $0.10/1M input and $0.30/1M output tokens on the cheapest tracked route. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads.
Pick Step 3.5 Flash for coding; token pricing is tied, so keep DeepSeek V3 only for already-validated prompts or route constraints.
Decision scorecard
Local evidence first| Signal | DeepSeek V3 | Step 3.5 Flash |
|---|---|---|
| Best for | tool-calling agents and provider-routed production | reasoning-heavy apps |
| Decision fit | Coding, Agents, and Classification | Coding, Agents, and Long context |
| Context window | 64k | 256k |
| Cheapest output | $0.30/1M tokens | $0.30/1M tokens |
| Provider routes | 13 tracked | 1 tracked |
| Shared benchmarks | 1 rows | LiveCodeBench leader |
Decision tradeoffs
- DeepSeek V3 has broader tracked provider coverage for fallback and procurement flexibility.
- DeepSeek V3 uniquely exposes Function calling, Tool use, and Structured outputs in local model data.
- Local decision data tags DeepSeek V3 for Coding, Agents, and Classification.
- Step 3.5 Flash holds a shared-benchmark lead on LiveCodeBench, ahead by 36.8 points.
- Step 3.5 Flash has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Step 3.5 Flash uniquely exposes Reasoning in local model data.
- 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 V3
$155
Cheapest tracked route/tier: Bitdeer AI
Step 3.5 Flash
$155
Cheapest tracked route/tier: OpenRouter
Estimated monthly gap: $0.00. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.
Switch friction
- Provider overlap exists on OpenRouter; start route-level A/B tests there.
- Cheapest tracked output pricing is tied, so migration risk shifts to quality, latency, and provider packaging.
- Check replacement coverage for Function calling, Tool use, and Structured outputs before moving production traffic.
- Step 3.5 Flash adds Reasoning in local capability data.
- Provider overlap exists on OpenRouter; start route-level A/B tests there.
- Cheapest tracked output pricing is tied, so migration risk shifts to quality, latency, and provider packaging.
- Check replacement coverage for Reasoning before moving production traffic.
- DeepSeek V3 adds Function calling, Tool use, and Structured outputs in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2024-12-26 | 2026-01-29 |
| Context window | 64k | 256k |
| Parameters | 671B | 196B (11B active) |
| Architecture | mixture of experts | mixture of experts |
| License | MIT(OSI) | Proprietary |
| Openness | Open source | Proprietary |
| Commercial use | Commercial use allowed | Commercial use with conditions |
| Knowledge cutoff | 2024-04 | - |
Pricing and availability
| Pricing attribute | DeepSeek V3 | Step 3.5 Flash |
|---|---|---|
| Input price | $0.10/1M tokens | $0.10/1M tokens |
| Output price | $0.30/1M tokens | $0.30/1M tokens |
| Providers |
Capabilities
| Capability | DeepSeek V3 | Step 3.5 Flash |
|---|---|---|
| Vision | No | No |
| Multimodal | No | No |
| Reasoning | No | Yes |
| Function calling | Yes | No |
| Tool use | Yes | No |
| Structured outputs | Yes | No |
| Code execution | No | No |
| IDE integration | No | No |
| Computer use | No | No |
| Parallel agents | No | No |
Benchmarks
| Benchmark | DeepSeek V3 | Step 3.5 Flash |
|---|---|---|
| LiveCodeBench | 49.6 | 86.4 |
Deep dive
On shared benchmark coverage, LiveCodeBench has DeepSeek V3 at 49.6 and Step 3.5 Flash at 86.4, with Step 3.5 Flash ahead by 36.8 points. The largest visible gap is 36.8 points on LiveCodeBench, which matters most when that benchmark mirrors your workload. Treat isolated benchmark wins as directional, because provider routing, prompt style, and tool access can move real application results.
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 $0.10/1M input and $0.30/1M 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 is tied on the cheapest tracked routes. Availability is 13 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.
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?
Neither is cheaper on tracked token pricing. Both list $0.10/1M input and $0.30/1M output tokens on the cheapest tracked route. Provider discounts, batch pricing, or route-specific tiers can still change the final bill.
Is DeepSeek V3 or Step 3.5 Flash open source?
DeepSeek V3 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 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.
Continue comparing
Last reviewed: 2026-05-29. Data sourced from public model cards and provider documentation.