Kimi K3 vs GPT-5.5 vs Claude Opus 4.8: which one should you use?
Kimi K3 is Moonshot AI's flagship model, announced in July 2026. The question everyone asks: how does it stack up against OpenAI's GPT-5.5 and Anthropic's Claude Opus 4.8? Here's an honest, source-linked comparison. The short version: all three play in the same top tier — the biggest difference is that K3 is open-weight and free to chat with, while the other two are closed and paid.
Quick comparison
| Kimi K3 | GPT-5.5 | Claude Opus 4.8 | |
|---|---|---|---|
| Maker | Moonshot AI | OpenAI | Anthropic |
| Open weights | Yes — free to download, self-host and fine-tune | No | No |
| Parameters | 2.8T total (MoE, 16 of 896 experts active) | Not disclosed | Not disclosed |
| Context window | 1M tokens | Large (see OpenAI docs) | Large (see Anthropic docs) |
| Free chat | Yes, on kimi.com and mobile apps | Limited free tier | Limited free tier |
| API pricing (input / output, per 1M tokens) | $3 / $15 ($0.30 with cache hit) — launch pricing | See OpenAI pricing | See Anthropic pricing |
Numbers above are as of July 2026, from official announcements and Artificial Analysis. Model specs and prices change fast — always double-check the linked sources before making a decision.
What the benchmarks say
According to Artificial Analysis (data checked July 2026), Kimi K3 scores in the same tier as GPT-5.5 and Claude Opus 4.8 on its Intelligence Index — notable because K3 is the only open-weight model in that tier. Benchmark results vary a lot by task and evaluation method, so treat any single ranking as a rough guide, not a verdict. For crowdsourced preferences, check LMArena.
Which one should you pick?
- Pick Kimi K3 if you want a top-tier model you can self-host or fine-tune, need a very long context window (1M tokens), or want strong performance at a lower API price. It's also the only one you can run on your own hardware.
- Pick GPT-5.5 if you're already invested in the OpenAI ecosystem (plugins, assistants, enterprise agreements) and don't need open weights.
- Pick Claude Opus 4.8 if your work leans on Anthropic's strengths — careful long-form writing, coding workflows inside Claude Code, or Anthropic-specific enterprise features.
For most people the honest answer is: try all three on your actual tasks. K3 makes that easy — it's free on kimi.com, no credit card needed.
Sources
Moonshot AI announcements via the Kimi blog · Kimi API documentation · Artificial Analysis Kimi K3 page · All links checked Jul 24, 2026. K3 Box is an independent directory, not affiliated with Moonshot AI, OpenAI or Anthropic.