Kimi K2 0905 is the September update of [Kimi K2 0711](moonshotai/kimi-k2). It is a large-scale Mixture-of-Experts (MoE) language model developed by Moonshot AI, featuring 1 trillion total parameters with 32 billion active per forward pass.…
Model details →MoonshotAI: Kimi K2 0905 (exacto) vs OpenAI: GPT-5.1-Codex
OpenAI: GPT-5.1-Codex wins on 3 of 6 axes — pricing and capability skew in its favour for most workloads.
GPT-5.1-Codex is a specialized version of GPT-5.1 optimized for software engineering and coding workflows. It is designed for both interactive development sessions and long, independent execution of complex engineering tasks. The model supp…
Model details →Side-by-side comparison
| Capability | MoonshotAI: Kimi K2 0905 (exacto) | OpenAI: GPT-5.1-Codex | Winner |
|---|---|---|---|
| Context window Maximum number of input tokens the model can attend to in a single request. | 262K | 400K | 🏆 OpenAI: GPT-5.1-Codex |
| Input price (per 1M) Cost per million input tokens billed by the provider. | $0.60 | $1.25 | 🏆 MoonshotAI: Kimi K2 0905 (exacto) |
| Output price (per 1M) Cost per million output tokens billed by the provider. | $2.50 | $10.00 | 🏆 MoonshotAI: Kimi K2 0905 (exacto) |
| Tool / function calling First-class support for emitting structured tool calls. | Yes | Yes | Tie |
| Vision input Accepts image inputs alongside text. | — | Yes | 🏆 OpenAI: GPT-5.1-Codex |
| Reasoning mode Internal chain-of-thought / extended-thinking support. | — | Yes | 🏆 OpenAI: GPT-5.1-Codex |
Frequently asked questions
Is MoonshotAI: Kimi K2 0905 (exacto) better than OpenAI: GPT-5.1-Codex?
OpenAI: GPT-5.1-Codex wins on 3 of 6 axes — pricing and capability skew in its favour for most workloads.
What's the price difference between MoonshotAI: Kimi K2 0905 (exacto) and OpenAI: GPT-5.1-Codex?
Input: $0.60 vs $1.25 per 1M tokens. Output: $2.50 vs $10.00 per 1M tokens.
What context windows do MoonshotAI: Kimi K2 0905 (exacto) and OpenAI: GPT-5.1-Codex support?
MoonshotAI: Kimi K2 0905 (exacto) supports up to 262K tokens. OpenAI: GPT-5.1-Codex supports up to 400K tokens.
Do both MoonshotAI: Kimi K2 0905 (exacto) and OpenAI: GPT-5.1-Codex support tool calling?
MoonshotAI: Kimi K2 0905 (exacto): yes. OpenAI: GPT-5.1-Codex: yes.