Kimi K2.6 vs Claude Sonnet 3.5 v2 vs Grok 4.20 (Reasoning)
Grok 4.20 (Reasoning) comes out ahead, 68 to 65 and 44 on our weighted score, and it is the cheaper option too.
Moonshot AIKimi K2.6
65/100- ECI151.1
- Price$0.95 / $4.00
- Context262K
AnthropicClaude Sonnet 3.5 v2
44/100- ECI133.5
- Price$3.00 / $15.00
- Context200K
- Our pick
xAIGrok 4.20 (Reasoning)
68/100- ECI152.0
- Price$1.25 / $2.50
- Context1M
Grok 4.20 (Reasoning) is our pick
Grok 4.20 (Reasoning) is the better all-round choice, scoring 68/100 against Kimi K2.6 (65) and Claude Sonnet 3.5 v2 (44). It leads on price and context window. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
- CapabilityGrok 4.20 (Reasoning)Capabilities Index (ECI): Grok 4.20 (Reasoning) 152.0 · Kimi K2.6 151.1 · Claude Sonnet 3.5 v2 133.5
- Lowest priceGrok 4.20 (Reasoning)Grok 4.20 (Reasoning) $1.56 · Kimi K2.6 $1.71 · Claude Sonnet 3.5 v2 $6.00 per 1M tokens (3:1 blend)
- Longest contextGrok 4.20 (Reasoning)Grok 4.20 (Reasoning) 1,000,000 · Kimi K2.6 262,144 · Claude Sonnet 3.5 v2 200,000 tokens
- Widest inputsSame inputsKimi K2.6: Text, Images, Video · Claude Sonnet 3.5 v2: Text, Images, PDFs · Grok 4.20 (Reasoning): Text, Images, PDFs
- Self-hostingKimi K2.6Publishes downloadable weights
| Measure | Weight | Kimi K2.6 | Claude Sonnet 3.5 v2 | Grok 4.20 (Reasoning) |
|---|---|---|---|---|
| CapabilityCapabilities Index (ECI) | 50% | 79 | 57 | 81 |
| Price | 25% | 39 | 13 | 41 |
| Inputs & features | 15% | 80 | 60 | 80 |
| Context window | 10% | 37 | 32 | 60 |
| Overall | 100% | 65/100 | 44/100 | 68/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Kimi K2.6Moonshot AI | Claude Sonnet 3.5 v2Anthropic | Grok 4.20 (Reasoning)xAI |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 151.1 | 133.5 | 152.0 (best) |
| ECI rank | #45 of 148 | #119 of 148 | #41 of 148 (best) |
| GPQA DiamondGraduate-level science questions | 90.8% (best) | 55.3% | 89.3% |
| FrontierMath Tiers 1–3Research-level mathematics | 57.2% (best) | — | 44.9% |
| OTIS Mock AIME 2024–2025Competition mathematics | 96.1% (best) | 8.5% | 92.2% |
| SWE-bench VerifiedFixing real GitHub issues | 76.7% | — | — |
| SimpleQA VerifiedShort factual questions | 34.9% (best) | — | 30.2% |
| Price per million tokens | |||
| Input | $0.95 (best) | $3.00 | $1.25 |
| Output | $4.00 | $15.00 | $2.50 (best) |
| Cached input | $0.16 (best) | — | $0.20 |
| Blended (3:1) | $1.71 | $6.00 | $1.56 (best) |
| Long-context rate | Same rate | Same rate | Over 200K: $2.50 / $5.00 |
| Price source | Official Moonshot AI API | Median of 1 providers | Official xAI API |
| Limits | |||
| Context window | 262,144 tokens | 200,000 tokens | 1,000,000 tokens (best) |
| Max output | 262,144 tokens (best) | 8,192 tokens | 30,000 tokens |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | No | Yes | Yes |
| Audio | No | No | No |
| Video | Yes | No | No |
| Reasoning | Yes | No | Yes |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | No | Yes |
| Availability | |||
| Weights | Open | Proprietary | Proprietary |
| API model ID | kimi-k2.6 | — | grok-4.20-0309-reasoning |
| API providers | 46 (best) | 1 | 11 |
| Released | Apr 21, 2026 | Oct 22, 2024 | Mar 9, 2026 |
| Knowledge cutoff | Jan 2025 | Apr 30, 2024 | — |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Kimi K2.6$17.50
- Claude Sonnet 3.5 v2$60.00
- Grok 4.20 (Reasoning)$17.50
Which should you choose?
Which is better: Kimi K2.6, Claude Sonnet 3.5 v2 or Grok 4.20 (Reasoning)?
Grok 4.20 (Reasoning) is the better all-round choice, scoring 68/100 against Kimi K2.6 (65) and Claude Sonnet 3.5 v2 (44). It leads on price and context window. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
Which is cheaper, Kimi K2.6, Claude Sonnet 3.5 v2 or Grok 4.20 (Reasoning)?
Grok 4.20 (Reasoning) is cheaper at $1.25 input / $2.50 output per million tokens (official xAI API price). Kimi K2.6 costs $0.95 input / $4.00 output per million tokens (official Moonshot AI API price); Claude Sonnet 3.5 v2 costs $3.00 input / $15.00 output per million tokens (median across 1 API provider). At a typical mix of three input tokens to one output token, that is $1.56 per million tokens for Grok 4.20 (Reasoning) versus $1.71 for Kimi K2.6 (1.1× as much) and $6.00 for Claude Sonnet 3.5 v2 (3.8× as much).
Which scores higher on benchmarks?
Grok 4.20 (Reasoning) scores higher on the Capabilities Index (ECI): Grok 4.20 (Reasoning) 152.0 (#41 of 148), Kimi K2.6 151.1 (#45 of 148) and Claude Sonnet 3.5 v2 133.5 (#119 of 148). The confidence ranges of the top two overlap (149.3–154.4 vs 149.1–152.8), so treat the gap as small. On individual benchmarks: GPQA Diamond — Kimi K2.6 90.8%, Grok 4.20 (Reasoning) 89.3%, Claude Sonnet 3.5 v2 55.3%; OTIS Mock AIME 2024–2025 — Kimi K2.6 96.1%, Grok 4.20 (Reasoning) 92.2%, Claude Sonnet 3.5 v2 8.5%.
Which is better for coding?
There are no published SWE-bench Verified results for Claude Sonnet 3.5 v2 and Grok 4.20 (Reasoning) yet, so there is no like-for-like coding score. On overall capability, Grok 4.20 (Reasoning) leads, which tends to carry over to coding, but test on your own codebase. All three support tool calling for agent workflows.
Which has the bigger context window?
Grok 4.20 (Reasoning) has the largest context window at 1,000,000 tokens, against 262,144 for Kimi K2.6 and 200,000 for Claude Sonnet 3.5 v2. Maximum output per response: Kimi K2.6 up to 262,144, Claude Sonnet 3.5 v2 up to 8,192, Grok 4.20 (Reasoning) up to 30,000 tokens.
Which can read images, PDFs, audio or video?
Kimi K2.6 accepts text, images and video; Claude Sonnet 3.5 v2 accepts text, images and PDFs; Grok 4.20 (Reasoning) accepts text, images and PDFs. They handle the same number of input types.
Are any of these open source?
Kimi K2.6 publishes its weights and can be self-hosted; Claude Sonnet 3.5 v2 and Grok 4.20 (Reasoning) is proprietary.
Which is newer?
Kimi K2.6 is the newest, released Apr 21, 2026. Grok 4.20 (Reasoning) came out Mar 9, 2026; Claude Sonnet 3.5 v2 came out Oct 22, 2024. Knowledge cutoff: Kimi K2.6 Jan 2025, Claude Sonnet 3.5 v2 Apr 30, 2024.
How do you decide the winner?
Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Oct 4, 2026.
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