GPT-5.6 Terra vs Muse Spark Open vs Kimi K3
Too close to call on our weighted score (Muse Spark Open 68, GPT-5.6 Terra 67, Kimi K3 65). The right pick depends on what you value most.
OpenAIGPT-5.6 Terra
67/100- ECI160.1
- Price$2.00 / $12.00
- Context1.05M
MetaMuse Spark Open
68/100- ECI155.1
- Price$1.25 / $4.25
- Context1.05M
Moonshot AIKimi K3
65/100- ECI158.3
- Price$3.00 / $15.00
- Context1.05M
Too close to call
It is close. Our weighted score puts them within a point (Muse Spark Open 68/100, GPT-5.6 Terra 67/100, Kimi K3 65/100), so choose by what matters most for your work: GPT-5.6 Terra for raw capability and Muse Spark Open on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
- CapabilityGPT-5.6 TerraCapabilities Index (ECI): GPT-5.6 Terra 160.1 · Kimi K3 158.3 · Muse Spark Open 155.1
- Lowest priceMuse Spark OpenMuse Spark Open $2.00 · GPT-5.6 Terra $4.50 · Kimi K3 $6.00 per 1M tokens (3:1 blend)
- Longest contextAbout the sameGPT-5.6 Terra 1,050,000 · Muse Spark Open 1,048,576 · Kimi K3 1,048,576 tokens
- Widest inputsMuse Spark OpenGPT-5.6 Terra: Text, Images, PDFs · Muse Spark Open: Text, Images, Audio, Video · Kimi K3: Text, Images, Video
- Self-hostingMuse Spark Open and Kimi K3Publishes downloadable weights (Muse Model License)
| Measure | Weight | GPT-5.6 Terra | Muse Spark Open | Kimi K3 |
|---|---|---|---|---|
| CapabilityCapabilities Index (ECI) | 50% | 89 | 83 | 87 |
| Price | 25% | 18 | 34 | 12 |
| Inputs & features | 15% | 80 | 80 | 80 |
| Context window | 10% | 61 | 61 | 61 |
| Overall | 100% | 67/100 | 68/100 | 65/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | GPT-5.6 TerraOpenAI | Muse Spark OpenMeta | Kimi K3Moonshot AI |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 160.1 (best) | 155.1 | 158.3 |
| ECI rank | #15 of 165 (best) | #39 of 165 | #20 of 165 |
| GPQA DiamondGraduate-level science questions | 93.3% (best) | 88.6% | 93.1% |
| FrontierMath Tiers 1–3Research-level mathematics | 86.0% (best) | 69.8% | 72.2% |
| OTIS Mock AIME 2024–2025Competition mathematics | 99.7% (best) | 98.1% | 97.2% |
| SimpleQA VerifiedShort factual questions | 43.2% | 56.6% (best) | 50.6% |
| Price per million tokens | |||
| Input | $2.00 | $1.25 (best) | $3.00 |
| Output | $12.00 | $4.25 (best) | $15.00 |
| Cached input | $0.20 (best) | — | $0.30 |
| Blended (3:1) | $4.50 | $2.00 (best) | $6.00 |
| Long-context rate | Over 272K: $4.00 / $18.00 | Same rate | Same rate |
| Price source | Official OpenAI API | Median of 16 providers | Official Moonshot AI API |
| Limits | |||
| Context window | 1,050,000 tokens (best) | 1,048,576 tokens | 1,048,576 tokens |
| Max output | 128,000 tokens | 131,072 tokens (best) | 131,072 tokens (best) |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | No | No |
| Audio | No | Yes | No |
| Video | No | Yes | Yes |
| Reasoning | Yeslow · medium · high · xhigh · max | Yes | Yeslow · high · max |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | No | Yes |
| Availability | |||
| Weights | Proprietary | OpenMuse Model License | Open |
| API model ID | gpt-5.6-terra | — | kimi-k3 |
| API providers | 45 | 16 | 76 (best) |
| Released | Jul 9, 2026 | Oct 15, 2026 | Jul 16, 2026 |
| Knowledge cutoff | Feb 16, 2026 | Jan 4, 2026 | — |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- GPT-5.6 Terra$44.00
- Muse Spark Open$21.00
- Kimi K3$60.00
Which should you choose?
Which is better: GPT-5.6 Terra, Muse Spark Open or Kimi K3?
It is close. Our weighted score puts them within a point (Muse Spark Open 68/100, GPT-5.6 Terra 67/100, Kimi K3 65/100), so choose by what matters most for your work: GPT-5.6 Terra for raw capability and Muse Spark Open on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
Which is cheaper, GPT-5.6 Terra, Muse Spark Open or Kimi K3?
Muse Spark Open is cheaper at $1.25 input / $4.25 output per million tokens (median across 16 API providers). GPT-5.6 Terra costs $2.00 input / $12.00 output per million tokens (official OpenAI API price); Kimi K3 costs $3.00 input / $15.00 output per million tokens (official Moonshot AI API price). At a typical mix of three input tokens to one output token, that is $2.00 per million tokens for Muse Spark Open versus $4.50 for GPT-5.6 Terra (2.3× as much) and $6.00 for Kimi K3 (3× as much).
Which scores higher on benchmarks?
GPT-5.6 Terra scores higher on the Capabilities Index (ECI): GPT-5.6 Terra 160.1 (#15 of 165), Kimi K3 158.3 (#20 of 165) and Muse Spark Open 155.1 (#39 of 165). The confidence ranges of the top two overlap (157.8–163.4 vs 155.8–161.4), so treat the gap as small. On individual benchmarks: GPQA Diamond — GPT-5.6 Terra 93.3%, Kimi K3 93.1%, Muse Spark Open 88.6%; FrontierMath Tiers 1–3 — GPT-5.6 Terra 86.0%, Kimi K3 72.2%, Muse Spark Open 69.8%; OTIS Mock AIME 2024–2025 — GPT-5.6 Terra 99.7%, Muse Spark Open 98.1%, Kimi K3 97.2%; SimpleQA Verified — Muse Spark Open 56.6%, Kimi K3 50.6%, GPT-5.6 Terra 43.2%.
Which is better for coding?
There are no published SWE-bench Verified results for GPT-5.6 Terra, Muse Spark Open and Kimi K3 yet, so there is no like-for-like coding score. On overall capability, GPT-5.6 Terra 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?
Their context windows are effectively the same size: GPT-5.6 Terra 1,050,000, Muse Spark Open 1,048,576 and Kimi K3 1,048,576 tokens. Maximum output per response: GPT-5.6 Terra up to 128,000, Muse Spark Open up to 131,072, Kimi K3 up to 131,072 tokens.
Which can read images, PDFs, audio or video?
GPT-5.6 Terra accepts text, images and PDFs; Muse Spark Open accepts text, images, audio and video; Kimi K3 accepts text, images and video. Muse Spark Open handles the widest range of inputs.
Are any of these open source?
Muse Spark Open and Kimi K3 publishes its weights (Muse Model License) and can be self-hosted; GPT-5.6 Terra is proprietary.
Which is newer?
Muse Spark Open is the newest, released Oct 15, 2026. Kimi K3 came out Jul 16, 2026; GPT-5.6 Terra came out Jul 9, 2026. Knowledge cutoff: GPT-5.6 Terra Feb 16, 2026, Muse Spark Open Jan 4, 2026.
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 Nov 2, 2026.
