> ## Documentation Index
> Fetch the complete documentation index at: https://docs.llmeasy.ru/llms.txt
> Use this file to discover all available pages before exploring further.

# Why can't Codex use GPT-5.5 in API mode?

> Temporarily enable GPT-5.5 in Codex custom API mode with a local model catalog.

As of April 24, 2026, some Codex versions may not let you select `gpt-5.5` directly when you use a custom API provider. This is a local model catalog limitation in Codex. It does not mean the LLMEasy `https://www.llmeasy.ru/v1` endpoint is unavailable.

You can add a local `custom-models.json` file so Codex can recognize `gpt-5.5`, then reference it from `~/.codex/config.toml`. If a later Codex version supports `gpt-5.5` natively, prefer the built-in Codex setup.

<Note>
  Use the complete `custom-models.json` provided on this page. If you edit the file manually, keep the existing model entries and fields, and only change the model configuration you need.
</Note>

## Setup steps

<Steps>
  <Step title="Prepare the custom model config file">
    The custom model config path is `~/.codex/custom-models.json`.

    <Tabs>
      <Tab title="Download JSON file">
        Download the complete model catalog:

        <a href="/images/downloads/custom-models-gpt-5.5.png" download="custom-models.json">Download custom-models.json</a>

        Put the downloaded file in the Codex config directory and name it `custom-models.json`.

        | System        | Target path                                    |
        | ------------- | ---------------------------------------------- |
        | macOS / Linux | `~/.codex/custom-models.json`                  |
        | Windows       | `C:\Users\YOUR_USER\.codex\custom-models.json` |

        The downloaded file is the complete model catalog. The next step references it from the Codex config.
      </Tab>

      <Tab title="Edit JSON manually">
        If you already have `~/.codex/custom-models.json`, edit the existing file. Do not keep only one `gpt-5.5` entry.

        When editing manually, confirm that the `models` array contains a `gpt-5.5` entry and keep the other model configs. If you are not familiar with JSON, use the download option.

        The `gpt-5.5` entry should include key fields similar to this:

        ```json theme={null}
        {
          "slug": "gpt-5.5",
          "display_name": "gpt-5.5",
          "description": "Custom local catalog entry for GPT-5.5 based on gpt-5.4 metadata.",
          "base_instructions": "...",
          "model_messages": {
            "instructions_template": "...",
            "instructions_variables": {
              "personality_default": "",
              "personality_friendly": "...",
              "personality_pragmatic": "..."
            }
          },
          "supports_reasoning_summaries": true,
          "support_verbosity": true,
          "context_window": 272000
        }
        ```

        <Note>
          The code block above only shows the key structure of a single model entry. Use the downloaded file or your existing complete model catalog as the source of truth.
        </Note>
      </Tab>
    </Tabs>
  </Step>

  <Step title="Reference the JSON file in Codex config">
    Open the Codex config file `~/.codex/config.toml`, then add or merge the following config.

    macOS / Linux example:

    ```toml theme={null}
    model_catalog_json = "/Users/YOUR_USER/.codex/custom-models.json"
    model_provider = "custom"
    model = "gpt-5.5"
    review_model = "gpt-5.4"
    model_reasoning_effort = "high"
    model_context_window = 1000000
    model_auto_compact_token_limit = 900000
    windows_wsl_setup_acknowledged = true

    [model_providers]
    [model_providers.custom]
    name = "LLM Easy"
    base_url = "https://www.llmeasy.ru/v1"
    wire_api = "responses"
    requires_openai_auth = false
    request_max_retries = 4
    stream_max_retries = 8
    stream_idle_timeout_ms = 300000
    supports_websockets = false
    ```

    Windows example:

    ```toml theme={null}
    model_catalog_json = "C:\\Users\\YOUR_USER\\.codex\\custom-models.json"
    ```

    `model_catalog_json` must be a local absolute path. In TOML double-quoted strings on Windows, write `\` as `\\`.
  </Step>

  <Step title="Restart Codex">
    After changing the config file, stop the current Codex process and start it in a new terminal session:

    ```bash theme={null}
    codex
    ```
  </Step>
</Steps>

## Troubleshooting

If `gpt-5.5` still does not work, check these items in order:

1. `model_catalog_json` uses a local absolute path
2. `custom-models.json` keeps the complete model catalog
3. `base_url` is `https://www.llmeasy.ru/v1`
4. `wire_api` is `responses`
5. `model_provider` matches the provider id in `[model_providers.custom]`

If your Codex version already supports `gpt-5.5` natively, remove `model_catalog_json` and return to the regular [Codex setup guide](/en/ai-tools/codex).