Side-by-side comparison of pricing, 12 benchmarks, and generation speed.
| Metric | DeepSeek V4 Flash (Reasoning, Max Effort) | Step 3.5 Flash 2603 |
|---|---|---|
| Input ($/M tokens) | $0.14 | $0.1 |
| Output ($/M tokens) | $0.28 | $0.3 |
Verdict. DeepSeek V4 Flash (Reasoning, Max Effort) wins the overall benchmark matchup 7–0 across 7 overlapping categories, but raw benchmark score is only one input to the decision.
Pricing. Both models sit in the budget bracket for output-token pricing. At 0.9× the per-million-token cost, DeepSeek V4 Flash (Reasoning, Max Effort) is meaningfully cheaper if your traffic is output-heavy (long completions, document generation, agent loops). DeepSeek V4 Flash (Reasoning, Max Effort) makes more sense when output volume is low and absolute reasoning quality justifies the premium.
Strengths. DeepSeek V4 Flash (Reasoning, Max Effort) is strongest on GPQA Diamond (89%), IFBench (79%), Coding Index (56.2). Step 3.5 Flash 2603 leads on GPQA Diamond (83%), IFBench (67%), SciCode (39%).
Speed. On throughput, Step 3.5 Flash 2603 generates tokens at 297 tok/s versus 118 tok/s — about 60% faster. On time-to-first-token, Step 3.5 Flash 2603 responds in 752ms vs 861ms, which matters most for chat-style UIs.
Provider. DeepSeek and StepFun sell to overlapping but distinct developer audiences: DeepSeek tends to ship frontier reasoning models with premium positioning, while StepFun often prices more aggressively. Your existing vendor relationships, billing, and SLA preferences may matter as much as the raw numbers above.
Workload cost. Workload scenarios (per million requests at 30M input + 15M output tokens): DeepSeek V4 Flash (Reasoning, Max Effort) costs $8.40 ($101/year); Step 3.5 Flash 2603 costs $7.50 ($90/year). At a smaller 5M-input/2M-output scale (single-developer tool or prototype): DeepSeek V4 Flash (Reasoning, Max Effort) ≈ $1.26/run, Step 3.5 Flash 2603 ≈ $1.10/run. At agent/realtime scale (200M input / 100M output per million requests): DeepSeek V4 Flash (Reasoning, Max Effort) ≈ $56/run, Step 3.5 Flash 2603 ≈ $50/run. Step 3.5 Flash 2603 becomes more attractive at higher volume — the absolute per-token pricing difference compounds when you ship at scale.
Recommendation. If you want one safe default, take DeepSeek V4 Flash (Reasoning, Max Effort) — it dominates the benchmark table and the latency profile is 2.5× faster. Step 3.5 Flash 2603 only makes sense when you specifically need its pricing tier, an existing contract, or a feature difference that is not measured by the benchmarks above.
Head-to-head deltas
Data from Artificial Analysis API — 12 benchmarks
Step 3.5 Flash 2603 is cheaper overall. Its blended price (3:1 input/output ratio) is $0.15/M tokens vs $0.17/M for DeepSeek V4 Flash (Reasoning, Max Effort).
DeepSeek V4 Flash (Reasoning, Max Effort) wins 7 out of 12 benchmarks compared to 0 for Step 3.5 Flash 2603. See the detailed benchmark chart above for per-category results.
Step 3.5 Flash 2603 generates tokens faster at 297 tok/s vs 118 tok/s. However, Step 3.5 Flash 2603 has lower time-to-first-token (0.75s vs 0.86s).
Choose based on your priorities: Step 3.5 Flash 2603 for lower cost, DeepSeek V4 Flash (Reasoning, Max Effort) for stronger benchmark performance, and Step 3.5 Flash 2603 for faster generation. For latency-sensitive apps, check the TTFT comparison above.