Claude Sonnet 4.5 vs Kimi K2.5
Claude Sonnet 4.5 (2025) and Kimi K2.5 (2026) are agentic coding models from Anthropic and Moonshot AI. Claude Sonnet 4.5 ships a 200K-token context window, while Kimi K2.5 ships a 256K-token context window. On MMLU PRO, Kimi K2.5 leads by 1.1 pts. On pricing, Kimi K2.5 costs $0.38/1M input tokens versus $3/1M for the alternative. This comparison covers specs, pricing, capabilities, benchmarks, provider availability, and production fit.
Kimi K2.5 is ~684% cheaper at $0.38/1M; pay for Claude Sonnet 4.5 only for reasoning depth.
Specs
| Released | 2025-09-29 | 2026-03-15 |
| Context window | 200K | 256K |
| Parameters | — | 1T (MoE, 384 experts) |
| Architecture | decoder only | mixture of experts |
| License | Proprietary | MIT |
| Knowledge cutoff | 2025-12 | - |
Pricing and availability
| Claude Sonnet 4.5 | Kimi K2.5 | |
|---|---|---|
| Input price | $3/1M tokens | $0.38/1M tokens |
| Output price | $15/1M tokens | $1.72/1M tokens |
| Providers |
Capabilities
| Claude Sonnet 4.5 | Kimi K2.5 | |
|---|---|---|
| Vision | ||
| Multimodal | ||
| Reasoning | ||
| Function calling | ||
| Tool use | ||
| Structured outputs | ||
| Code execution |
Benchmarks
| Benchmark | Claude Sonnet 4.5 | Kimi K2.5 |
|---|---|---|
| MMLU PRO | 86.0 | 87.1 |
| Massive Multi-discipline Multimodal Understanding | 77.8 | 84.3 |
| BFCL | 73.2 | 68.3 |
Deep dive
On shared benchmark coverage, MMLU PRO has Claude Sonnet 4.5 at 86 and Kimi K2.5 at 87.1, with Kimi K2.5 ahead by 1.1 points; Massive Multi-discipline Multimodal Understanding has Claude Sonnet 4.5 at 77.8 and Kimi K2.5 at 84.3, with Kimi K2.5 ahead by 6.5 points; BFCL has Claude Sonnet 4.5 at 73.2 and Kimi K2.5 at 68.3, with Claude Sonnet 4.5 ahead by 4.9 points. The largest visible gap is 6.5 points on Massive Multi-discipline Multimodal Understanding, which matters most when that benchmark mirrors your workload. Treat isolated benchmark wins as directional, because provider routing, prompt style, and tool access can move real application results.
The capability footprint differs most on vision: Claude Sonnet 4.5, multimodal input: Claude Sonnet 4.5, reasoning mode: Claude Sonnet 4.5, and tool use: Claude Sonnet 4.5. Both models share function calling and structured outputs, 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, Claude Sonnet 4.5 lists $3/1M input and $15/1M output tokens, while Kimi K2.5 lists $0.38/1M input and $1.72/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts Kimi K2.5 lower by about $5.82 per million blended tokens. Availability is 8 providers versus 7, so concentration risk also matters.
Choose Claude Sonnet 4.5 when reasoning depth and broader provider choice are central to the workload. Choose Kimi K2.5 when coding workflow support, larger context windows, 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.
FAQ
Which has a larger context window, Claude Sonnet 4.5 or Kimi K2.5?
Kimi K2.5 supports 256K tokens, while Claude Sonnet 4.5 supports 200K tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
Which is cheaper, Claude Sonnet 4.5 or Kimi K2.5?
Kimi K2.5 is cheaper on tracked token pricing. Claude Sonnet 4.5 costs $3/1M input and $15/1M output tokens. Kimi K2.5 costs $0.38/1M input and $1.72/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is Claude Sonnet 4.5 or Kimi K2.5 open source?
Claude Sonnet 4.5 is listed under Proprietary. Kimi K2.5 is listed under MIT. 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 vision, Claude Sonnet 4.5 or Kimi K2.5?
Claude Sonnet 4.5 has the clearer documented vision signal in this comparison. If vision is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Which is better for multimodal input, Claude Sonnet 4.5 or Kimi K2.5?
Claude Sonnet 4.5 has the clearer documented multimodal input signal in this comparison. If multimodal input is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Where can I run Claude Sonnet 4.5 and Kimi K2.5?
Claude Sonnet 4.5 is available on Microsoft Foundry, Anthropic, Snowflake Cortex, GCP Vertex AI, and AWS Bedrock. Kimi K2.5 is available on Fireworks AI, OpenRouter, Together AI, Fireworks AI, and NVIDIA NIM. 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.