Chinese text resolves to a heavier font weight than Latin text on macOS

What version of the Codex App are you using (From “About Codex” dialog)?

Codex Desktop 26.616.81150 (build 4306)

What subscription do you have?

ChatGPT Plus

What platform is your computer?

Darwin 25.5.0 arm64 arm

Additional environment details:

• macOS 26.5.1 (25F80)
• MacBook Air (Mac15,13)
• Apple M3
• 16 GB memory

What issue are you seeing?

In Codex Desktop on macOS, Chinese text appears noticeably heavier than Latin text in mixed-language conversation content when using the default UI font settings.

This makes Chinese and English text within the same paragraph look visually unbalanced. The issue is most apparent in the main conversation body, but other UI text using the same typography settings may be affected.

I investigated the rendered conversation UI using the Chrome DevTools Protocol (CDP).

The main conversation text inherits its font weight from the global VS Code typography variable. The relevant CSS is effectively:

.app-theme {
  --vscode-font-weight: 430;
}

body {
  font-weight: var(--vscode-font-weight);
}

Consequently, the conversation body is rendered with:

font-weight: 430;

CDP platform-font inspection of mixed Chinese and Latin text showed:

Latin:
familyName: .SF NS
postScriptName: .SFNS-Regular_..._wght...
requested font-weight: 430

Chinese:
familyName: PingFang SC
postScriptName: PingFangSC-Medium
requested font-weight: 430

Apple’s Latin system font is variable and can represent 430 through continuous wght-axis interpolation. Its visual increase from Regular is therefore subtle.

For Chinese glyphs, the same requested weight resolves to the discrete PingFangSC-Medium face. This produces a much larger, step-like visual increase:

Latin 430 → subtle variable-weight interpolation
Chinese 430 → discrete jump from Regular to Medium

This is a font-weight matching issue rather than a missing-font fallback issue: both scripts receive the same requested CSS weight, but that weight produces substantially different visual results.

A minimal Chromium browser test reproduced the behavior outside the Codex component structure:

font-family: -apple-system, BlinkMacSystemFont, sans-serif;
font-weight: 400; /* Chinese renders as PingFangSC-Regular */

font-weight: 401; /* Chinese may resolve as PingFangSC-Medium */

Changing the requested weight from 400 to 401 caused a pronounced step in Chinese text, while Latin text changed only subtly.

As a runtime experiment, overriding the inherited weight to 400 caused Chinese text to resolve as PingFangSC-Regular and restored a much more balanced appearance without changing the configured font family.

What steps can reproduce the bug?

1. Open Codex Desktop on macOS.
2. Keep the default UI font settings.
3. Open a conversation containing mixed Chinese and English text.
4. Observe that Chinese glyphs appear significantly heavier than adjacent Latin glyphs within the same text style.
5. Inspect the conversation body and confirm that it inherits font-weight: 430.
6. Temporarily override the inherited weight to 400.
7. Observe that the Chinese text becomes visually coordinated with the Latin text.

The same behavior may occur in other UI regions that inherit --vscode-font-weight: 430.

What is the expected behavior?

Chinese and Latin text in mixed-language conversation content should have visually coordinated weights under the default UI font settings while preserving the current Latin typography.

The investigation above describes the observed rendering behavior and does not prescribe a particular implementation or fix.

Additional information

No custom UI font is required to reproduce this issue. It occurs with Codex Desktop’s default UI font settings on macOS.