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Kimi Open Platform natively supports the Responses API used by Codex, so Codex can use the kimi-k3 model directly — no protocol conversion or local proxy is required.
Codex CLI supports text and image input, but does not provide a native video input channel — you cannot submit a video file directly as multimodal input to the model. This is a limitation of Codex CLI’s input layer, not of the Kimi K3 model — the Kimi K3 API natively supports video input. Call kimi-k3 directly as described in Vision Input for full video understanding, with no manual frame extraction required.

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Prerequisites

Before you start, complete the following preparations. Follow the corresponding official instructions for installation and account-related operations; this guide does not repeat those procedures.

Install Codex CLI

Follow the official Codex documentation and start Codex CLI at least once. To use the Codex desktop app, download it from the official site or run codex app after installing the CLI.

Create an API key

Create and save an API key in Kimi Open Platform.

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Step 1: Configure the API key

Codex reads the API key from an environment variable. Do not write the key into config.toml. To keep the key out of your shell history, enter it as follows:
This only applies to the current terminal session. To persist it, add the export command to ~/.zshrc (or ~/.bashrc if you use bash on Linux). The file stores the key in plain text — set permissions accordingly.

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Step 2: Add Kimi as a model provider

Open ~/.codex/config.toml (on Windows: %USERPROFILE%\.codex\config.toml) and add the following configuration. If model or model_provider already exist, replace their values:

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Use Codex Desktop

After completing the API key and provider configuration above, quit and restart Desktop so it reloads ~/.codex/config.toml. After Desktop starts, open the model picker and select kimi-k3. The interface may show Custom, but requests still use the kimi-k3 you configured. The Desktop composer shows the "Custom" model label Send a simple request like hi — a normal reply means the basic connection works: Kimi replies to a simple greeting in Desktop Next, send a task that exercises Codex’s agent capabilities:
If Desktop continues generating a final answer after the tool results come back, model calls and tool calling are working properly.

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Use Codex CLI

Codex CLI shares the same user-level configuration as Desktop, so the configuration above applies to it as well. Enter your project directory and start Codex (if Codex CLI is already running, exit the current session first so it reloads the configuration):
After startup, confirm that Codex CLI shows kimi-k3 as the current model: Confirm kimi-k3 as the current model in Codex CLI Send a simple request (for example hello). A normal reply confirms that Codex is connected through the Kimi Responses API. Under the hood, Codex sends requests to POST https://api.moonshot.ai/v1/responses. For request and response schema details, see the Responses API reference.

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Troubleshooting

The API key is invalid, or the key and the base_url belong to different platforms — API keys created on platform.kimi.ai only work with https://api.moonshot.ai/v1. Also confirm that KIMI_API_KEY is available in the environment used to start Codex or Desktop. For CLI, check it in the terminal where you start Codex with test -n "$KIMI_API_KEY" && echo set || echo missing.
The request includes the search_context_size parameter, which is not supported yet — remove it. Codex does not send this parameter by default, and the built-in web_search tool works out of the box.
base_url is wrong — make sure it is exactly https://api.moonshot.ai/v1 (with the /v1 suffix). If you previously connected through CC Switch or another local router, also confirm base_url no longer points at a local address such as http://127.0.0.1:....
You have hit a rate or concurrency limit. See Rate limits for your tier’s quotas.
kimi-k3 is not in Codex’s built-in model catalog. This warning is expected and does not affect usage — the model_context_window = 1048576 from Step 2 already ensures the context window is treated as 1M.
Codex only reads config.toml at startup — exit and restart it. Also confirm you edited ~/.codex/config.toml itself and that no -c flags or profiles are overriding it. If you previously connected through CC Switch, also turn off Codex under its Settings > Routing — otherwise it keeps rewriting config.toml and overwrites the new configuration.
See Error codes for the meaning of each status code.