[BUG] timeFormat: "12-hour" setting is not passed to the model; model outputs 24-hour times

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

The user-level timeFormat setting is honored by the Claude Code UI but is never
passed to the model. The model therefore writes times in 24-hour format in its
replies, contradicting the user's configured preference.

What Should Happen?

Description

The user-level timeFormat setting is honored by the Claude Code UI but is never
passed to the model. The model therefore writes times in 24-hour format in its
replies, contradicting the user's configured preference.

Environment

• Claude Code: 2.1.285
• OS: macOS 27.0 (locale en_US)
• Setting in ~/.claude/settings.json: "timeFormat": "12-hour"

Error Messages/Logs

Steps to Reproduce

Steps to reproduce

1. Set "timeFormat": "12-hour" in ~/.claude/settings.json.
2. Start a session and ask for a time estimate or a "done by" time.

Expected

The model writes times in 12-hour format ("done around 1:50 am"), consistent with
the user's setting, without the user having to repeat the preference.

Actual

The model writes 24-hour times ("done around 20:30"). When asked why, it stated it
"can't see that setting". The setting is not included in the model's context,
even though the settings file is readable from the session.

Related

In the same session the model also quoted estimates from a stale or wrong clock
(hours off from the local time), for the same reason: no reliable local
time or format context is provided to it.

Suggested fix

Include user display preferences (timeFormat, and the local timezone) in the
model's context, the same way other environment facts are provided.

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.285

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

_No response_