Kimi K3.1 Pro vs Claude Opus 5.5

Short answer: neither wins at everything.

Pick Kimi K3.1 Pro if you want a brand-new model aimed at long coding sessions and agent tasks, and can live with launch hiccups.

Pick Claude Opus 5.5 if you need the strongest Claude for long documents, writing and coding.

Kimi K3.1 Pro vs Claude Opus 5.5 side by side

	Kimi K3.1 Pro	Claude Opus 5.5
What it is	Model from Moonshot AI (China)	Anthropic's top model
Made by	Moonshot AI (Kimi)	Anthropic
Price	Developer price: $2 in (output price not verified) per million tokens	Developer price: $4 in and $20 out per million tokens
Good at	Ranked near the top of Artificial Analysis's index on Oct 27 (rankings are relative; see our note). 1,048,576-token context (Kimi docs); Best for: long coding sessions, agent tasks, knowledge work; Reads up to 1,048,576 tokens at once	Hector's pick for long documents and writing; Best for: long documents, writing, coding; Reads up to 1,000,000 tokens at once; Reads: text, image, PDFs
Watch out for	Launch had rate-limit and quota problems; Moonshot apologized and reset 25% of subscribers' quota (Oct 25); Input price $2/M is from Simon Willison's Oct 23 post and matches Artificial Analysis; Kimi's own pricing table did not load for us, so it's not verified there. Output price not verified.	Not listed in our data
Where it runs	Kimi app (kimi.ai)	Claude Pro/Max
Status	Current. Launched Oct 23, 2026 on the Kimi app and Kimi developer service, with a faster K3.1 Pro Highspeed version. Moonshot says full model weights will be released by Nov 4, 2026 (not yet open as of Oct 27). Kimi's older K2 models close to new users Oct 31 and retire by end of Dec 2026.	Current. Retirement not sooner than Sep 22, 2027. Fast mode (up to ~2.5x faster output, $8/$40 per million tokens) is open to all developer service users since Oct 15, 2026
Sources	kimi.ai · platform.kimi.ai · platform.moonshot.ai · simonwillison.net · artificialanalysis.ai	platform.claude.com · claude.com · models.dev · platform.claude.com (2) · platform.claude.com (3)

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Questions people ask

Is Kimi K3.1 Pro or Claude Opus 5.5 better?

It depends on what you do. Pick Kimi K3.1 Pro if you want a brand-new model aimed at long coding sessions and agent tasks, and can live with launch hiccups. Pick Claude Opus 5.5 if you need the strongest Claude for long documents, writing and coding.

How does WhichBot decide?

Hector uses a written rubric: everyday usefulness, cost and free plans, privacy, reliability, ease of use, availability and safety. Rankings are one input, not the answer.

Facts come from the companies' own pages, linked above, and were last checked Oct 28, 2026. Prices are US and can change. Picks are Hector's: no paid picks, sponsors always labeled, and no sponsorship from AI labs. Our policy.