Kimi K3 vs Muse Spark Open

Two models head to head

Kimi K3 and Muse Spark Open are two open-weight models that you can install on your own servers, one from Moonshot AI, the other from Meta. Kimi K3 was released on July 16, 2026, Muse Spark Open on October 15, 2026.

All figures below come from public sources checked on October 22, 2026: models.dev and OpenRouter for prices and capabilities, Epoch AI for scores.

Which one is more capable?

On our capability index, Kimi K3 scores 80.7 out of 100 and Muse Spark Open 75.2. Kimi K3 leads by 5.5 points.

On the 4 benchmarks reported for both, Kimi K3 wins 3 times and Muse Spark Open 1:

• GPQA Diamond (PhD-level science questions): Kimi K3 93.1%, Muse Spark Open 88.6%
• OTIS Mock AIME (competition mathematics problems): Kimi K3 97.2%, Muse Spark Open 98.1%
• FrontierMath (very hard research-level mathematics): Kimi K3 72.2%, Muse Spark Open 69.8%
• APEX-Agents (professional tasks carried out by an agent): Kimi K3 47.8%, Muse Spark Open 33.4%

Budget

Kimi K3 costs $3 per million input tokens and $15 per million output tokens; Muse Spark Open costs $1.25 and $4.25.

For a typical agent task (read 20,000 tokens, write 2,000), expect $0.09 with Kimi K3 versus $0.034 with Muse Spark Open. Muse Spark Open is 2.7 times cheaper, a gap that adds up quickly over 1,000 tasks: $56.5 difference.

Run the numbers with your own volumes in the agent cost calculator.

Context and capabilities

Both models have the same context window: 1,048,576 tokens, roughly 1,573 pages.

Reasoning mode: Kimi K3 yes, Muse Spark Open yes. Tool calling: Kimi K3 yes, Muse Spark Open yes. Image input: Kimi K3 yes, Muse Spark Open yes.

Both publish their weights: you can host them yourself.

In short

Our reading of the data:

• Choose Kimi K3 for a higher capability index.
• Choose Muse Spark Open for a lower cost and a more recent release.

This verdict relies on public figures; it does not replace a trial on your own tasks.