Step 5 Preview Explained

Step 5 Preview is StepFun's flagship model for agentic work, built on a sparse Mixture-of-Experts (MoE) architecture with 600B total parameters, 27B active parameters, and a 1.0M-token context window. On OpenRouter, Step 5 Preview is listed at $1 per 1M input tokens and $2.70 per 1M output tokens, with prompt cache read requests priced at $0.05 per 1M tokens. StepFun released it on October 8, 2026. OpenRouter says it is strong in software engineering and professional knowledge work, particularly finance.

OpenRouter lists one provider, StepFun. A Reddit r/LocalLLaMA thread titled 'StepFun Step 5 preview showing up in openrouter' also noted the listing. A StepFun tweet titled 'StepFun opens Step5 Preview free for a week through OpenCode, Cline and Kilo Code' says it is free for a week through OpenCode, Cline and Kilo Code; we read only the title, so the terms and end date are unknown.

What Step 5 Preview Is and What It Costs

Step 5 Preview is StepFun's flagship agentic model, priced on OpenRouter at $1.00 per 1M input tokens and $2.70 per 1M output tokens. Prompt cache reads are billed at $0.05 per 1M tokens. Step 5 Preview supports a 1.0M-token context window and was launched on October 8, 2026.

OpenRouter lists a single backend provider for the model, which is StepFun itself. OpenRouter forwards every request directly to StepFun infrastructure. At the listed rates, 500,000 input tokens cost $0.50, or $0.025 as a cache read; 10,000 output tokens cost $0.027.

Direct StepFun pricing outside OpenRouter is unknown to us, so use OpenRouter's listed rates as the baseline.

• Input token price: $1.00 per 1M tokens.
• Output token price: $2.70 per 1M tokens.
• Prompt cache read price: $0.05 per 1M tokens.
• Context window capacity: 1.0M tokens.
• Hosting path: OpenRouter forwards requests directly to StepFun.

Architecture Mechanics of a Sparse Mixture of Experts

In a sparse Mixture-of-Experts model, only part of the parameters work on each token: 27B of 600B here. Per-token compute is therefore closer to a 27B model than a 600B one. OpenRouter lists no cost per task, so measure that on your own prompts.

StepFun manages this hosting directly, with OpenRouter forwarding every request. We could not confirm whether the weights are open.

• Total parameter scale: 600B parameters across the model network.
• Active parameters: 27B weights engaged per token during inference.
• Hardware management: StepFun hosts the model directly.

Managing Tasks across the 1.0M Token Context Window

A 1.0M-token context window gives Step 5 Preview room for large codebases and documents. OpenRouter describes the model as built for extended tasks that span large codebases and documents.

OpenRouter lists cache reads at $0.05 per 1M tokens, 5% of the $1.00 input rate. OpenRouter's page does not say which requests qualify, so check a test run's billing.

Domain Strengths in Engineering and Professional Knowledge Work

OpenRouter says Step 5 Preview performs strongly in software engineering and professional knowledge work, with particular strength in finance. It is designed for extended tasks that use tools and refine results over multiple steps.

We found no benchmark scores for Step 5 Preview, so test it on your own tasks.

• Software engineering and professional knowledge work, particularly finance (OpenRouter's description).
• Extended tasks using tools and refining results over multiple steps.
• Benchmark availability: no published benchmark scores.

Accessing the StepFun API through OpenRouter

Developers can access Step 5 Preview through OpenRouter using an OpenAI-compatible Application Programming Interface (API) schema. OpenRouter's API is OpenAI-compatible, and only the model slug changes between models: stepfun/step-5-preview.

OpenRouter currently lists a single provider for this endpoint, forwarding all completions directly to StepFun's servers.

StepFun highlighted promotional availability in a tweet titled 'StepFun opens Step5 Preview free for a week through OpenCode, Cline and Kilo Code' on its official account. The post was shared as a title only, so the terms and end date are unknown. Verify the promotion terms on the StepFun tweet before testing.

Operational Latency and Throughput Metrics

OpenRouter reports a p50 latency of 3.50 seconds and a generation throughput of 55 tokens per second for Step 5 Preview. Latency and throughput are as shown on OpenRouter at fetch time; the 100.00% uptime covers 3 days.

Deploying Step 5 Preview in Business Workflows

Businesses can pilot Step 5 Preview on coding-agent or document-analysis tasks. At $1.00 per million input tokens, teams can trial passing large repositories into context during multi-step agent runs.

Run the same tasks on Step 5 Preview and on your current model, and compare cost per task.

Keep a fallback model configured. Because StepFun is currently the sole provider listed on OpenRouter for this model, any provider outage would stall processing unless your client fails over to another model, for example GLM-5.3. A rise in OpenRouter's price, or throughput below the listed 55 tokens/s, would change this advice.

• Coding-agent task: trial the model on a bounded coding workflow.
• Document-analysis task: trial the model on a document workflow.
• Cost per task vs your current model: compare spend on the same prompts.
• Fallback model: keep a secondary model configured in case of provider downtime.

Step 5 Preview Verification and Workflow Testing Steps

Teams adopting Step 5 Preview should treat the release as an experimental preview and verify production viability against proprietary prompt sets. The name includes 'Preview', so pricing, limits and behavior may change. Skip it if you need published benchmarks or more than one provider. Confirm current pricing directly on the OpenRouter model page before provisioning large batch workloads.

At Layer3Labs, we build custom agents and integrations for small and mid-sized businesses.

Start by testing a small set of repository tickets against the OpenRouter endpoint, track token consumption and task completion rates against your current baseline, and measure whether Step 5 Preview delivers lower operational costs for your team.