Claude Sonnet 5.5 vs Kimi K2.6: a data-driven comparison

Side-by-side comparison

Criterion	Claude Sonnet 5.5	Kimi K2.6
Developer	Anthropic	Moonshot AI
Released	September 28, 2026	April 20, 2026
Capability index	95.9 / 100	84.4 / 100
Input price	$2	$0.95
Output price	$10	$4
Cost of a typical task	$0.06	$0.027
Context window	1,000,000 tokens	262,144 tokens
Maximum output	128,000 tokens	262,144 tokens
Reasoning mode	Yes	Yes
Tool calling	Yes	Yes
Accepted inputs	text, image, PDF	text, image, video
Open weights	No	Yes
Knowledge cutoff	June 2026	January 2025

Two models head to head

This comparison pits the flagship models of two major developers against each other: Claude Sonnet 5.5 and Kimi K2.6, one from Anthropic, the other from Moonshot AI. The first dates from September 28, 2026, the second from April 20, 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 Kimi K2.6 84.4. Claude Sonnet 5.5 leads by 11.5 points.

On the 3 benchmarks reported for both, Claude Sonnet 5.5 wins 3 times and Kimi K2.6 0:

GPQA Diamond (PhD-level science questions): Claude Sonnet 5.5 95.6%, Kimi K2.6 90.8%
OTIS Mock AIME (competition mathematics problems): Claude Sonnet 5.5 100%, Kimi K2.6 96.1%
FrontierMath (very hard research-level mathematics): Claude Sonnet 5.5 88.8%, Kimi K2.6 57.2%

Which one costs less?

Claude Sonnet 5.5 costs $2 per million input tokens and $10 per million output tokens; Kimi K2.6 costs $0.95 and $4.

For a typical agent task (read 20,000 tokens, write 2,000), expect $0.06 with Claude Sonnet 5.5 versus $0.027 with Kimi K2.6. Kimi K2.6 is 2.2 times cheaper, a gap that adds up quickly over 1,000 tasks: $33 difference.

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

Under the hood

Claude Sonnet 5.5 reads more in one go: 1,000,000 tokens of context (roughly 1,500 pages), versus 262,144 for Kimi K2.6.

Reasoning mode: Claude Sonnet 5.5 yes, Kimi K2.6 yes. Tool calling: Claude Sonnet 5.5 yes, Kimi K2.6 yes. Image input: Claude Sonnet 5.5 yes, Kimi K2.6 yes.

Kimi K2.6 publishes its weights and can run on your servers; Claude Sonnet 5.5 is a closed model, available only through an API.

Knowledge cutoff: June 2026 for Claude Sonnet 5.5, January 2025 for Kimi K2.6.

In short

Our reading of the data:

Choose Claude Sonnet 5.5 for a higher capability index, a larger context window and a more recent release.
Choose Kimi K2.6 for a lower cost and open weights (you can host it yourself).

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

Frequently asked questions

Claude Sonnet 5.5 or Kimi K2.6: which is better?

On our index (Epoch AI data), Claude Sonnet 5.5 scores 95.9 and Kimi K2.6 84.4 out of 100. The best choice also depends on price and on your use case.

Which one is cheaper?

Kimi K2.6. To read 20,000 tokens and write 2,000, expect $0.06 with Claude Sonnet 5.5 and $0.027 with Kimi K2.6 (prices as of October 22, 2026).

Which one has the larger context window?

Claude Sonnet 5.5, with 1,000,000 tokens versus 262,144.

Can I run Claude Sonnet 5.5 or Kimi K2.6 on my own servers?

Only Kimi K2.6, whose weights are published. Claude Sonnet 5.5 is used through an API.

Claude Sonnet 5.5 versus Kimi K2.6