Claude Sonnet 5.5 versus Muse Spark 1.3

What are we comparing?

Claude Sonnet 5.5 and Muse Spark 1.3 are the flagship models of two major developers, one from Anthropic, the other from Meta. Claude Sonnet 5.5 was released on September 28, 2026, Muse Spark 1.3 on September 2, 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.

Performance

On our capability index, Claude Sonnet 5.5 scores 95.9 out of 100 and Muse Spark 1.3 82.7. Claude Sonnet 5.5 leads by 13.2 points.

On the 3 benchmarks reported for both, Claude Sonnet 5.5 wins 3 times and Muse Spark 1.3 0:

• OTIS Mock AIME (competition mathematics problems): Claude Sonnet 5.5 100%, Muse Spark 1.3 99.2%
• FrontierMath (very hard research-level mathematics): Claude Sonnet 5.5 88.8%, Muse Spark 1.3 74.4%
• APEX-Agents (professional tasks carried out by an agent): Claude Sonnet 5.5 75.5%, Muse Spark 1.3 58.6%

Pricing

Claude Sonnet 5.5 costs $2 per million input tokens and $10 per million output tokens; Muse Spark 1.3 costs $0.10 and $0.20.

For a typical agent task (read 20,000 tokens, write 2,000), expect $0.06 with Claude Sonnet 5.5 versus $0.002 with Muse Spark 1.3. Muse Spark 1.3 is 25 times cheaper, a gap that adds up quickly over 1,000 tasks: $57.6 difference.

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

Features and limits

Muse Spark 1.3 reads more in one go: 1,048,576 tokens of context (roughly 1,573 pages), versus 1,000,000 for Claude Sonnet 5.5.

Reasoning mode: Claude Sonnet 5.5 yes, Muse Spark 1.3 yes. Tool calling: Claude Sonnet 5.5 yes, Muse Spark 1.3 yes. Image input: Claude Sonnet 5.5 yes, Muse Spark 1.3 yes.

Neither publishes its weights: both are used through an API.

In short

Our reading of the data:

• Choose Claude Sonnet 5.5 for a higher capability index.
• Choose Muse Spark 1.3 for a lower cost.

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