Does Day One work on iPhone Duo?

Yes. Day One is updated for iPhone Duo and uses the full inner display. Its latest version is built with the iOS 27.1 SDK and uses Apple’s iPhone Duo APIs.

Is Day One letterboxed on iPhone Duo?

No. Day One fills the inner display.

All apps

Day One

Name: Day One: Daily Journal & Diary
Author: Bloom Built Inc

Bloom Built IncUtilities

View in the App Store

On iPhone Duo

Fits

Day One fills the inner screen and adapts when you fold.

Its latest version is built with the iOS 27.1 SDK and uses Apple’s iPhone Duo APIs.[1]

How we know: From the app’s build
Checked on: Version 2026.22
Build: iOS 27.1 SDK
uses Apple’s iPhone Duo APIs
Latest version: 2026.22, Oct 23, 2026
Status updated: Oct 28, 2026

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Version history

Version 2026.22Fits
iOS 27.1 SDK
Checked Oct 28, 2026

Sources

App Store build, version 2026.22
Built with the iOS 27.1 SDK. Uses SwiftUI’s toolbarVerticalEdge.
App Store: Day One 2026.22 release notes