DeepSeek: DeepSeek V3.1 vs StepFun: Step 3.5 Flash: Live Promos, Pricing, Hidden Fees & Latency
Verified 2026 FinOps benchmark comparing DeepSeek: DeepSeek V3.1 (deepseek/deepseek-chat-v3.1) vs StepFun: Step 3.5 Flash (stepfun/step-3.5-flash). Simulate cache read multipliers, context cliffs, MAU bills, and P90 latency.
DeepSeek: DeepSeek V3.1 (deepseek/deepseek-chat-v3.1) — Automatic Disk KV Cache ($0.125/1M) & Off-Peak Promo
DeepSeek-V4 Pro (1.6T MoE) automatically caches repeated 64-token prompt prefixes on NVMe storage at $0.07/1M input tokens (50% off $0.14 base) with zero code changes required, plus off-peak UTC scheduling discounts.
StepFun: Step 3.5 Flash (stepfun/step-3.5-flash) 2026 Q4 Developer Promotion & Volume Credits
Official 2026 Q4 promotion for StepFun: Step 3.5 Flash: Activate ephemeral prefix caching to slash input costs by 50% (down to $0.05/1M) or route via asynchronous Batch API for 50% off standard token rates.
In Etuki October 2026 FinOps telemetry comparing DeepSeek: DeepSeek V3.1 (API ID: deepseek/deepseek-chat-v3.1) vs StepFun: Step 3.5 Flash (API ID: stepfun/step-3.5-flash), StepFun: Step 3.5 Flash offers lower standard input pricing at $0.1/1M tokens ($0.3/1M output), while StepFun: Step 3.5 Flash leads in cached prefix economics at $0.05/1M tokens (50% discount). DeepSeek: DeepSeek V3.1 achieves a 0ms faster P90 time-to-first-token latency (280ms vs 280ms).
Auto-discovered via live global telemetry registry.
Auto-discovered via live global telemetry registry.
| Specification / FinOps Dimension | DeepSeek: DeepSeek V3.1 | StepFun: Step 3.5 Flash | Verified Advantage |
|---|---|---|---|
| Official Vendor API ID | deepseek/deepseek-chat-v3.1 | stepfun/step-3.5-flash | Pinned Snapshot IDs |
| Standard Input / Output (per 1M) | $0.25 / $0.95 | $0.1 / $0.3 | StepFun: Step 3.5 Flash |
| Cache Read Price (per 1M) | $0.125/1M (50% Off) | $0.05/1M (50% Off) | StepFun: Step 3.5 Flash |
| Context Window / Max Output | 160K In / 32K Out | 256K In / 64K Out | StepFun: Step 3.5 Flash |
| P90 First-Token / Edge Latency | 280ms | 280ms | DeepSeek: DeepSeek V3.1 (-0ms) |
DeepSeek-V3.1 is a large hybrid reasoning model (671B parameters, 37B active) that supports both thinking and non-thinking modes via prompt templates. It extends the DeepSeek-V3 ba
Step 3.5 Flash is StepFun's most capable open-source foundation model. Built on a sparse Mixture of Experts (MoE) architecture, it selectively activates only 11B of its 196B parame
Real-Time Stack Cost & Hidden-Fee Simulator (MAU / Token / Egress / GMV)
Calibrated with Reddit r/FinOps & r/devops telemetry: Includes Context Caching, Bandwidth Egress, and MoR Tax
🛰️Switch from DeepSeek: DeepSeek V3.1 to StepFun: Step 3.5 Flash
Step 3.5 Flash is StepFun's most capable open-source foundation model. Built on a sparse Mixture of Experts (MoE) architecture, it selectively activates only 11B of its 196B parame Verified P90 latency of 280ms.