Kimi K2.5 vs Step 3.5 Flash
Kimi K2.5 (2026) and Step 3.5 Flash (2026) are agentic coding models from Moonshot AI and StepFun. Kimi K2.5 ships a 256K-token context window, while Step 3.5 Flash ships a 256K-token context window. On pricing, Step 3.5 Flash costs $0.1/1M input tokens versus $0.38/1M for the alternative. This comparison covers specs, pricing, capabilities, benchmarks, provider availability, and production fit. It focuses on practical selection signals rather than broad model-family marketing.
Step 3.5 Flash is ~283% cheaper at $0.1/1M; pay for Kimi K2.5 only for coding workflow support.
Specs
| Released | 2026-03-15 | 2026-01-29 |
| Context window | 256K | 256K |
| Parameters | 1T (MoE, 384 experts) | 196B (11B active) |
| Architecture | mixture of experts | mixture of experts |
| License | MIT | Open Source |
| Knowledge cutoff | - | - |
Pricing and availability
| Kimi K2.5 | Step 3.5 Flash | |
|---|---|---|
| Input price | $0.38/1M tokens | $0.1/1M tokens |
| Output price | $1.72/1M tokens | $0.3/1M tokens |
| Providers |
Capabilities
| Kimi K2.5 | Step 3.5 Flash | |
|---|---|---|
| Vision | ||
| Multimodal | ||
| Reasoning | ||
| Function calling | ||
| Tool use | ||
| Structured outputs | ||
| Code execution |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on reasoning mode: Step 3.5 Flash, function calling: Kimi K2.5, and structured outputs: Kimi K2.5. 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, Kimi K2.5 lists $0.38/1M input and $1.72/1M output tokens, while Step 3.5 Flash lists $0.1/1M input and $0.3/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts Step 3.5 Flash lower by about $0.62 per million blended tokens. Availability is 7 providers versus 1, so concentration risk also matters.
Choose Kimi K2.5 when coding workflow support and broader provider choice are central to the workload. Choose Step 3.5 Flash when reasoning depth and lower input-token cost are more important. For production, rerun your own prompts through the exact provider, region, and tool stack you plan to ship. This keeps the decision grounded in measurable tradeoffs instead of brand-level assumptions. It also helps separate model capability from provider packaging, which can change cost and latency.
FAQ
Which has a larger context window, Kimi K2.5 or Step 3.5 Flash?
Kimi K2.5 supports 256K tokens, while Step 3.5 Flash supports 256K tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
Which is cheaper, Kimi K2.5 or Step 3.5 Flash?
Step 3.5 Flash is cheaper on tracked token pricing. Kimi K2.5 costs $0.38/1M input and $1.72/1M output tokens. Step 3.5 Flash costs $0.1/1M input and $0.3/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is Kimi K2.5 or Step 3.5 Flash open source?
Kimi K2.5 is listed under MIT. Step 3.5 Flash is listed under Open Source. 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, Kimi K2.5 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, Kimi K2.5 or Step 3.5 Flash?
Kimi K2.5 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 Kimi K2.5 and Step 3.5 Flash?
Kimi K2.5 is available on Fireworks AI, OpenRouter, Together AI, Fireworks AI, and NVIDIA NIM. Step 3.5 Flash is available on OpenRouter. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
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Last reviewed: 2026-04-27. Data sourced from public model cards and provider documentation.