Claude Sonnet 5 vs Kimi K2 Thinking
AnthropicMoonshot AIboth via one key, provider price + 3%
Claude Sonnet 5 (Anthropic, released 2026-06-30) and Kimi K2 Thinking (Moonshot AI, released 2025-11-06) sit at opposite ends of the price/capability curve. Sonnet 5 supports images and files, runs a 1M-token context window, and posts an artificial_analysis coding index of 71.5. Kimi K2 Thinking is text-only, caps context at 262,144 tokens, and always runs in reasoning mode. Both are available on OpenKey through one API key with a flat 3% fee on top of provider list price.
Spec vs spec
| Spec | Claude Sonnet 5 | Kimi K2 Thinking |
|---|---|---|
| Context window | 1M | 262K |
| Max output | 128K | 100K |
| Input modalities | text, image, file | text |
| Output modalities | text | text |
| Released | Jun 30, 2026 | Nov 6, 2025 |
| Reasoning | optional | always on |
Pricing
Per 1M tokens. Provider price plus the flat 3% fee — the sum is what you pay.
anthropic/claude-sonnet-5
Input · 1M tokens
$2.00 + 3%$2.06
Output · 1M tokens
$10.00 + 3%$10.30
Cache read · 1M tokens
$0.200 + 3%$0.206
Cache write · 1M tokens
$2.50 + 3%$2.58
FEE — FLAT, EVERY MODEL3%
moonshotai/kimi-k2-thinking
Input · 1M tokens
$0.600 + 3%$0.618
Output · 1M tokens
$2.50 + 3%$2.58
Cache read · 1M tokens
$0.150 + 3%$0.154
FEE — FLAT, EVERY MODEL3%
One workload, priced on both
10M input + 2M output tokens at each model's price, flat 3% fee included.
anthropic/claude-sonnet-5
$41.20
$40.00 provider + 3%
moonshotai/kimi-k2-thinkingCheaper
$11.33
$11.00 provider + 3%
Pricing math on a real workload
Provider list price: Sonnet 5 is $2.00/M input, $10.00/M output. Kimi K2 Thinking is $0.60/M input, $2.50/M output. On OpenKey that's provider price × 1.03 — Sonnet 5 becomes $2.06/M input and $10.30/M output; Kimi K2 Thinking becomes $0.618/M input and $2.575/M output.
For a 10M-input / 2M-output workload, computed cost comes out to **$40.00 for Sonnet 5** vs **$11.00 for Kimi K2 Thinking** — Sonnet 5 costs roughly 3.6x more for that same workload. The input price ratio alone is 3.33x. If you're running high-token-volume batch jobs (RAG pipelines, bulk summarization), that ratio compounds fast.
Coding and agentic performance
This is where the two models diverge hardest. Sonnet 5 scores 71.5 on the artificial_analysis coding index and 46.7 on agentic index, against Kimi K2 Thinking's 21 and 1.8 respectively. Overall intelligence index is 53.4 for Sonnet 5 vs 17.3 for Kimi K2 Thinking. Kimi K2 Thinking does have a Design Arena entry — 1156 elo, 48.8% win rate, rank 70 in the 'website' category — but Sonnet 5 has no Design Arena data in this record, so that's not a direct comparison point. For agent loops, tool-calling reliability, and multi-step coding tasks, the artificial_analysis gap is the number that matters.
Context window and modality
Sonnet 5 handles text, images, and files with a 1,000,000-token context window and a 128,000-token max completion. Kimi K2 Thinking is text-only, with a 262,144-token context window and a 100,352-token max completion — a context ratio of 3.81x in Sonnet 5's favor. If your workload involves multi-modal input (screenshots, PDFs) or you need to hold very large documents in context, Sonnet 5 is the only option of the two. If your input is plain text and fits under 262K tokens, the context advantage doesn't matter.
Reasoning behavior
Kimi K2 Thinking's reasoning is mandatory — every response runs through its reasoning process, with no way to turn it off. Sonnet 5's reasoning is optional, with five selectable effort levels (low, medium, high, xhigh, max) and a default of medium, so you can dial cost and latency up or down per request. That flexibility matters if you're mixing simple lookups with complex agent tasks in the same pipeline — you don't want to pay max-effort reasoning cost for a trivial call.
Which model for which job
| Use case | Pick | Why |
|---|---|---|
| Production coding agent | Claude Sonnet 5 | 71.5 coding index vs 21, plus 46.7 agentic index vs 1.8 |
| High-volume batch text processing | Kimi K2 Thinking | $11 vs $40 for a 10M-in/2M-out workload |
| Multi-modal input (images, PDFs) | Claude Sonnet 5 | Kimi K2 Thinking is text-only; Sonnet 5 takes text, image, and file input |
| Very long document analysis | Claude Sonnet 5 | 1M-token context vs 262,144 tokens — a 3.81x wider window |
| Cost-sensitive reasoning tasks at scale | Kimi K2 Thinking | Input price is $0.618/M on OpenKey vs $2.06/M for Sonnet 5 |
| Variable-complexity request mix | Claude Sonnet 5 | Selectable reasoning effort (low to max) vs Kimi's mandatory reasoning on every call |
Questions
- Which model is cheaper for a typical workload?
- Kimi K2 Thinking, by a wide margin. On a 10M-input / 2M-output workload, Kimi K2 Thinking costs $11.00 total versus $40.00 for Claude Sonnet 5 — roughly a 3.6x difference. The input price ratio alone is 3.33x in Kimi K2 Thinking's favor.
- Which model is better for coding?
- Claude Sonnet 5. It scores 71.5 on the artificial_analysis coding index versus 21 for Kimi K2 Thinking — more than 3x higher. Its agentic index (46.7 vs 1.8) also points to more reliable multi-step tool use, which matters for coding agents specifically.
- Can Kimi K2 Thinking handle images or files?
- No. Kimi K2 Thinking is text-only (input and output). Claude Sonnet 5 accepts text, image, and file input, so if your task involves screenshots or document uploads, Sonnet 5 is the only one of the two that works.
- Do both models work through the same API key?
- Yes. Both Claude Sonnet 5 and Kimi K2 Thinking run on OpenKey with one API key, and pricing is the provider's list price plus a flat 3% fee — for example Sonnet 5's $2.00/M input becomes $2.06/M, and Kimi K2 Thinking's $0.60/M input becomes $0.618/M.