Kimi K2 vs Step 3.5 Flash
Kimi K2 (2025) and Step 3.5 Flash (2026) are frontier reasoning models from Moonshot AI and StepFun. Kimi K2 ships a 262k-token context window, while Step 3.5 Flash ships a 256k-token context window. On pricing, Step 3.5 Flash costs $0.10/1M input tokens versus $0.50/1M 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 ~400% cheaper at $0.10/1M; pay for Kimi K2 only for long-context analysis.
Decision scorecard
Local evidence first| Signal | Kimi K2 | Step 3.5 Flash |
|---|---|---|
| Best for | tool-calling agents and provider-routed production | reasoning-heavy apps |
| Decision fit | RAG, Agents, and Long context | Long context |
| Context window | 262k | 256k |
| Cheapest output | $2/1M tokens | $0.30/1M tokens |
| Provider routes | 3 tracked | 1 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- Kimi K2 has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Kimi K2 has broader tracked provider coverage for fallback and procurement flexibility.
- Kimi K2 uniquely exposes Function calling and Structured outputs in local model data.
- Local decision data tags Kimi K2 for RAG, Agents, and Long context.
- Step 3.5 Flash has the lower cheapest tracked output price at $0.30/1M tokens.
- Step 3.5 Flash uniquely exposes Reasoning in local model data.
- Local decision data tags Step 3.5 Flash for Long context.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output route or tier on this page.
Kimi K2
$900
Cheapest tracked route/tier: AWS Bedrock
Step 3.5 Flash
$155
Cheapest tracked route/tier: OpenRouter
Estimated monthly gap: $745. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.
Switch friction
- Provider overlap exists on OpenRouter; start route-level A/B tests there.
- Step 3.5 Flash is $1.70/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Check replacement coverage for Function calling and Structured outputs before moving production traffic.
- Step 3.5 Flash adds Reasoning in local capability data.
- Provider overlap exists on OpenRouter; start route-level A/B tests there.
- Kimi K2 is $1.70/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- Check replacement coverage for Reasoning before moving production traffic.
- Kimi K2 adds Function calling and Structured outputs in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2025-07-11 | 2026-01-29 |
| Context window | 262k | 256k |
| Parameters | 1K | 196B (11B active) |
| Architecture | - | mixture of experts |
| License | Proprietary | Open Source |
| Knowledge cutoff | - | - |
Pricing and availability
| Pricing attribute | Kimi K2 | Step 3.5 Flash |
|---|---|---|
| Input price | $0.50/1M tokens | $0.10/1M tokens |
| Output price | $2/1M tokens | $0.30/1M tokens |
| Providers |
Capabilities
| Capability | Kimi K2 | Step 3.5 Flash |
|---|---|---|
| Vision | No | No |
| Multimodal | No | No |
| Reasoning | No | Yes |
| Function calling | Yes | No |
| Tool use | No | No |
| Structured outputs | Yes | No |
| Code execution | No | No |
| IDE integration | No | No |
| Computer use | No | No |
| Parallel agents | No | No |
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, and structured outputs: Kimi K2. 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 lists $0.50/1M input and $2/1M output tokens on the cheapest tracked provider, while Step 3.5 Flash lists $0.10/1M input and $0.30/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts Step 3.5 Flash lower by about $0.79 per million blended tokens. Availability is 3 providers versus 1, so concentration risk also matters.
Choose Kimi K2 when long-context analysis, larger context windows, 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.
FAQ
Which has a larger context window, Kimi K2 or Step 3.5 Flash?
Kimi K2 supports 262k 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 or Step 3.5 Flash?
Step 3.5 Flash is cheaper on tracked token pricing. Kimi K2 costs $0.50/1M input and $2/1M output tokens. Step 3.5 Flash costs $0.10/1M input and $0.30/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is Kimi K2 or Step 3.5 Flash open source?
Kimi K2 is listed under Proprietary. 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 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 or Step 3.5 Flash?
Kimi K2 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 and Step 3.5 Flash?
Kimi K2 is available on OpenRouter, AWS Bedrock, and GCP Vertex AI. 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: 2026-05-29. Data sourced from public model cards and provider documentation.