Circadian Rhythm & Sleep: ARCv2.0.0

What changed

• UXComplete rebuild of the app engine and home screen interface to a plan-based layout.
• New featureDynamic caffeine cutoff calculation based on bedtime, metabolism, and real-time logging.
• New featureNew learning algorithm that tracks and predicts the user's afternoon energy dip.
• New featureIntroduction of Trends tab to track weekly crashes, light habits, and cutoff adherence.
• New featureWeekly Experiments feature to test and score behavioral changes over five days.
• ContentExpanded Learn tab with eight new briefings and updated scientific claims.
• New featureNew logging capabilities for movement, rest, and focus with the ability to undo logs.
• PlatformAdded Home screen widgets and Live Activity support for morning light tracking.
• LocalizationFull German language localization support.
• UXEnhanced settings for 12/24-hour clock, chronotype, and caffeine sensitivity.

Original release notes

ARC 2.0 is a rebuild, not a coat of paint.

1.8 told you true things about circadian rhythm. 2.0 tells you about today, using your own numbers — and then shows its working.

YOUR DAY, AS A PLAN
The home screen is now one sentence, one ask, and the rest of your day underneath it. Blocks close when you log what closes them, and the plan re-times itself when the day does not go as expected.

A CUTOFF THAT IS ACTUALLY YOURS
Your last safe coffee used to be a fixed offset from waking. It is now solved from your bedtime, your caffeine metabolism and everything you have drunk today — so it
moves the moment you log a cup.

IT LEARNS YOUR DIP
Tell us when you crash and we will use it. After about ten days of check-ins we use the hour you actually crash instead, and tell you if the two differ.

TRENDS
Crashes per week and whether they are falling. When your dip really lands. How often you held morning light and your cutoff — and what each one changed.

WEEKLY EXPERIMENTS
One change, five days, scored against the fortnight before. Including when the answer is "no difference".

LEARN IS STILL HERE
The Intel tab is now Learn, with all fifteen briefings kept and eight new ones added — the afternoon dip, why your cutoff moves, fast and slow caffeine metabolisers, crossing time zones, alcohol, and light in winter. We also went through the older pieces and removed every claim we could not stand behind.

MOVEMENT, REST AND FOCUS
Now loggable whether or not the app asked. Any log can be taken back.

WIDGETS AND LOCK SCREEN
Home screen widgets carry your own phase colours and your next ask. The morning light timer runs as a Live Activity, so your phone can stay in your pocket while
you are outside.

YOUR HISTORY COMES WITH YOU
Everything you logged in 1.8 — energy, light, wake and sleep times — is carried into the new engine, so Trends starts with the history you already have rather than from zero.

Also: German throughout, a 12/24-hour setting that follows your device, and editable wake time, bedtime, chronotype and caffeine sensitivity in Settings
without resetting anything.