StepFun: Step 3.5 Flash vs Anthropic Claude Sonnet 5.5: Live Promos, Pricing, Hidden Fees & Latency
Verified 2026 FinOps benchmark comparing StepFun: Step 3.5 Flash (stepfun/step-3.5-flash) vs Anthropic Claude Sonnet 5.5 (claude-sonnet-5-5). Simulate cache read multipliers, context cliffs, MAU bills, and P90 latency.
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.
Sonnet 5.5 High-Velocity Coding Promo: $0.10/1M Cached Input & $1/$5 Batch Tier
Anthropic's September/October 2026 rollout prices Claude Sonnet 5.5 at half of Opus 5.5 ($2/$10) while activating $0.10/1M (0.05x) cached input reads and $1.00/$5.00 asynchronous batch processing.
In Etuki October 2026 FinOps telemetry comparing StepFun: Step 3.5 Flash (API ID: stepfun/step-3.5-flash) vs Anthropic Claude Sonnet 5.5 (API ID: claude-sonnet-5-5), 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). Anthropic Claude Sonnet 5.5 achieves a 50ms faster P90 time-to-first-token latency (230ms vs 280ms).
Auto-discovered via live global telemetry registry.
Enable Prompt Context Caching & Batch API to reduce repeated system prompt input token burn by 50%-97.5%.
| Specification / FinOps Dimension | StepFun: Step 3.5 Flash | Anthropic Claude Sonnet 5.5 | Verified Advantage |
|---|---|---|---|
| Official Vendor API ID | stepfun/step-3.5-flash | claude-sonnet-5-5 | Pinned Snapshot IDs |
| Standard Input / Output (per 1M) | $0.1 / $0.3 | $2 / $10 | StepFun: Step 3.5 Flash |
| Cache Read Price (per 1M) | $0.05/1M (50% Off) | $0.1/1M (95% Off) | StepFun: Step 3.5 Flash |
| Context Window / Max Output | 256K In / 64K Out | 1000K In / 128K Out | Anthropic Claude Sonnet 5.5 |
| P90 First-Token / Edge Latency | 280ms | 230ms | Anthropic Claude Sonnet 5.5 (-50ms) |
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
Released Sept 28, 2026 at half of Opus 5.5 price with 0.05x ($0.10/1M) cache reads for high-speed SWE agents.
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 StepFun: Step 3.5 Flash to Anthropic Claude Sonnet 5.5
Released Sept 28, 2026 at half of Opus 5.5 price with 0.05x ($0.10/1M) cache reads for high-speed SWE agents. Verified P90 latency of 230ms.