Which is cheaper, Claude Opus 5.5 and Kimi K3.1 Pro?

Kimi K3.1 Pro has the lowest input price. Per 1M input tokens: Claude Opus 5.5 from $4.00 and Kimi K3.1 Pro from $2.00.

Which has the larger context window, Claude Opus 5.5 and Kimi K3.1 Pro?

Kimi K3.1 Pro has the largest context window: Claude Opus 5.5 1,000,000 tokens and Kimi K3.1 Pro 1,048,576 tokens.

Which is smarter, Claude Opus 5.5 and Kimi K3.1 Pro?

Claude Opus 5.5 scores highest on the Artificial Analysis Intelligence Index: Claude Opus 5.5 58.4 and Kimi K3.1 Pro 46.0.

Can I switch between Claude Opus 5.5 and Kimi K3.1 Pro without changing my code?

Yes. All of them are served through FastRouter's OpenAI-compatible API, so switching is a change of the model parameter (anthropic/claude-opus-5.5, moonshotai/kimi-k3.1-pro).

Claude Opus 5.5 vs Kimi K3.1 Pro

Side-by-side pricing per provider, context window, benchmark scores and speed, all on one OpenAI-compatible API.

Estimate monthly cost for these models

Claude Opus 5.5 Anthropicanthropic/claude-opus-5.5

Kimi K3.1 Pro MoonshotAImoonshotai/kimi-k3.1-pro

Creator

Anthropic

MoonshotAI

Released

Sep 22, 2026

Oct 23, 2026

Context window

1.05M

Max output

128K

1.05M

Input / 1MLowest provider price

$4.00

$2.00

Output / 1MLowest provider price

$20.00

$10.00

Providers

IntelligenceArtificial Analysis index

58.4

46.0

Accepts

Text, Image, Files

Text, Image

Produces

Text

Tool calling

Yes

Structured output

Yes

Reasoning

Yes

Claude Opus 5.5 vs Kimi K3.1 Pro: summary

Claude Opus 5.5 and Kimi K3.1 Pro are both available through FastRouter's OpenAI-compatible API, so switching between them is a change of model id, not a new integration.

Claude Opus 5.5, from Anthropic, has a 1,000,000-token context window, costs from $4.00/1M input and $20.00/1M output tokens across 3 providers and scores 58.4 on the Artificial Analysis Intelligence Index.

Kimi K3.1 Pro, from MoonshotAI, has a 1,048,576-token context window, costs $2.00/1M input and $10.00/1M output tokens and scores 46.0 on the Artificial Analysis Intelligence Index.

Kimi K3.1 Pro is the cheapest on input, 2× cheaper than the next model, Kimi K3.1 Pro has the largest context window and Claude Opus 5.5 scores highest for intelligence.

Switch with one line

client = OpenAI(base_url="https://api.fastrouter.ai/api/v1", api_key="<FASTROUTER_API_KEY>") client.chat.completions.create(model="anthropic/claude-opus-5.5", messages=[...]) # or client.chat.completions.create(model="moonshotai/kimi-k3.1-pro", messages=[...])

Full API docs

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More comparisons

Benchmark scores sourced from ArtificialAnalysis