Grok 4.20 (Reasoning) vs Gemini 3.5 Flash vs Kimi K2.6
Too close to call on our weighted score (Gemini 3.5 Flash 69, Grok 4.20 (Reasoning) 68, Kimi K2.6 65). The right pick depends on what you value most.
xAIGrok 4.20 (Reasoning)
68/100- ECI152.0
- Price$1.25 / $2.50
- Context1M
GoogleGemini 3.5 Flash
69/100- ECI154.5
- Price$1.50 / $9.00
- Context1.05M
Moonshot AIKimi K2.6
65/100- ECI151.1
- Price$0.95 / $4.00
- Context262K
Too close to call
It is close. Our weighted score puts them within a point (Gemini 3.5 Flash 69/100, Grok 4.20 (Reasoning) 68/100, Kimi K2.6 65/100), so choose by what matters most for your work: Gemini 3.5 Flash for raw capability and Grok 4.20 (Reasoning) on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
- CapabilityGemini 3.5 FlashCapabilities Index (ECI): Gemini 3.5 Flash 154.5 · Grok 4.20 (Reasoning) 152.0 · Kimi K2.6 151.1
- Lowest priceGrok 4.20 (Reasoning)Grok 4.20 (Reasoning) $1.56 · Kimi K2.6 $1.71 · Gemini 3.5 Flash $3.38 per 1M tokens (3:1 blend)
- Longest contextGemini 3.5 FlashGemini 3.5 Flash 1,048,576 · Grok 4.20 (Reasoning) 1,000,000 · Kimi K2.6 262,144 tokens
- Widest inputsGemini 3.5 FlashGrok 4.20 (Reasoning): Text, Images, PDFs · Gemini 3.5 Flash: Text, Images, PDFs, Audio, Video · Kimi K2.6: Text, Images, Video
- Self-hostingKimi K2.6Publishes downloadable weights
| Measure | Weight | Grok 4.20 (Reasoning) | Gemini 3.5 Flash | Kimi K2.6 |
|---|---|---|---|---|
| CapabilityCapabilities Index (ECI) | 50% | 81 | 84 | 79 |
| Price | 25% | 41 | 25 | 39 |
| Inputs & features | 15% | 80 | 100 | 80 |
| Context window | 10% | 60 | 61 | 37 |
| Overall | 100% | 68/100 | 69/100 | 65/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Grok 4.20 (Reasoning)xAI | Gemini 3.5 FlashGoogle | Kimi K2.6Moonshot AI |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 152.0 | 154.5 (best) | 151.1 |
| ECI rank | #41 of 148 | #33 of 148 (best) | #45 of 148 |
| GPQA DiamondGraduate-level science questions | 89.3% | 92.8% (best) | 90.8% |
| FrontierMath Tiers 1–3Research-level mathematics | 44.9% | 62.8% (best) | 57.2% |
| OTIS Mock AIME 2024–2025Competition mathematics | 92.2% | 95.6% | 96.1% (best) |
| SWE-bench VerifiedFixing real GitHub issues | — | 79.3% (best) | 76.7% |
| SimpleQA VerifiedShort factual questions | 30.2% | 66.2% (best) | 34.9% |
| Price per million tokens | |||
| Input | $1.25 | $1.50 | $0.95 (best) |
| Output | $2.50 (best) | $9.00 | $4.00 |
| Cached input | $0.20 | $0.15 (best) | $0.16 |
| Blended (3:1) | $1.56 (best) | $3.38 | $1.71 |
| Long-context rate | Over 200K: $2.50 / $5.00 | Same rate | Same rate |
| Price source | Official xAI API | Official Google API | Official Moonshot AI API |
| Limits | |||
| Context window | 1,000,000 tokens | 1,048,576 tokens (best) | 262,144 tokens |
| Max output | 30,000 tokens | 65,536 tokens | 262,144 tokens (best) |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | Yes | No |
| Audio | No | Yes | No |
| Video | No | Yes | Yes |
| Reasoning | Yes | Yesminimal · low · medium · high | Yes |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | Yes | Yes |
| Availability | |||
| Weights | Proprietary | Proprietary | Open |
| API model ID | grok-4.20-0309-reasoning | gemini-3.5-flash | kimi-k2.6 |
| API providers | 11 | 32 | 46 (best) |
| Released | Mar 9, 2026 | May 19, 2026 | Apr 21, 2026 |
| Knowledge cutoff | — | Jan 2025 | Jan 2025 |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Grok 4.20 (Reasoning)$17.50
- Gemini 3.5 Flash$33.00
- Kimi K2.6$17.50
Which should you choose?
Which is better: Grok 4.20 (Reasoning), Gemini 3.5 Flash or Kimi K2.6?
It is close. Our weighted score puts them within a point (Gemini 3.5 Flash 69/100, Grok 4.20 (Reasoning) 68/100, Kimi K2.6 65/100), so choose by what matters most for your work: Gemini 3.5 Flash for raw capability and Grok 4.20 (Reasoning) on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
Which is cheaper, Grok 4.20 (Reasoning), Gemini 3.5 Flash or Kimi K2.6?
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); Gemini 3.5 Flash costs $1.50 input / $9.00 output per million tokens (official Google API price). 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 $3.38 for Gemini 3.5 Flash (2.2× as much).
Which scores higher on benchmarks?
Gemini 3.5 Flash scores higher on the Capabilities Index (ECI): Gemini 3.5 Flash 154.5 (#33 of 148), Grok 4.20 (Reasoning) 152.0 (#41 of 148) and Kimi K2.6 151.1 (#45 of 148). The confidence ranges of the top two overlap (152.5–156.6 vs 149.3–154.4), so treat the gap as small. On individual benchmarks: GPQA Diamond — Gemini 3.5 Flash 92.8%, Kimi K2.6 90.8%, Grok 4.20 (Reasoning) 89.3%; FrontierMath Tiers 1–3 — Gemini 3.5 Flash 62.8%, Kimi K2.6 57.2%, Grok 4.20 (Reasoning) 44.9%; OTIS Mock AIME 2024–2025 — Kimi K2.6 96.1%, Gemini 3.5 Flash 95.6%, Grok 4.20 (Reasoning) 92.2%; SimpleQA Verified — Gemini 3.5 Flash 66.2%, Kimi K2.6 34.9%, Grok 4.20 (Reasoning) 30.2%.
Which is better for coding?
There are no published SWE-bench Verified results for Grok 4.20 (Reasoning) yet, so there is no like-for-like coding score. On overall capability, Gemini 3.5 Flash 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?
Gemini 3.5 Flash has the largest context window at 1,048,576 tokens, against 1,000,000 for Grok 4.20 (Reasoning) and 262,144 for Kimi K2.6. Maximum output per response: Grok 4.20 (Reasoning) up to 30,000, Gemini 3.5 Flash up to 65,536, Kimi K2.6 up to 262,144 tokens.
Which can read images, PDFs, audio or video?
Grok 4.20 (Reasoning) accepts text, images and PDFs; Gemini 3.5 Flash accepts text, images, PDFs, audio and video; Kimi K2.6 accepts text, images and video. Gemini 3.5 Flash handles the widest range of inputs.
Are any of these open source?
Kimi K2.6 publishes its weights and can be self-hosted; Grok 4.20 (Reasoning) and Gemini 3.5 Flash is proprietary.
Which is newer?
Gemini 3.5 Flash is the newest, released May 19, 2026. Kimi K2.6 came out Apr 21, 2026; Grok 4.20 (Reasoning) came out Mar 9, 2026. Knowledge cutoff: Gemini 3.5 Flash Jan 2025, Kimi K2.6 Jan 2025.
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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