C1M Duo

Everyone who uses ChatGPT and Claude knows the dance: ask one, copy the answer, paste it into the other, ask "is this right?". Duo does that dance for you — on the phone, in one tap.

ChatGPT answers. Claude checks it and fixes what's wrong. You get one answer that opens with three short blocks — where both agree, where they differ, what to check yourself — on screen, in the clipboard and in a journal file in iCloud Drive, in about a minute.

• Runs on the ChatGPT and Claude apps you already have, through their official Ask ChatGPT and Ask Claude actions — no server, no API keys

• Free accounts are enough; if you already have Plus or Pro, the strongest models of two companies work together at no extra cost

• 12 modes in one shortcut: Critique (default), Debate until agreement, Dispute map, Synthesis, Side by side, Decision, Debate, Advisor, Clarify, Delta, Image, Auto — the ✉ badge shows each mode's message cost before you pick

• Put it on the Action Button, Back Tap or Siri and it becomes a "second opinion" button

• 11 languages: English, Español, Português, Русский, Українська, Deutsch, Français, हिन्दी, 日本語, 한국어, 中文

• Any iPhone on iOS 18 or later — an iPhone 14 runs it fine

This has existed on computers — browser extensions, paid AI hubs, API setups. On a phone, free, with no gateway in between, there was nothing like it until now.

Requirements: iOS 18+, the ChatGPT and Claude apps installed and signed in. First run: tap "Always Allow" each time it asks (4–6 times). Don't touch the screen while it runs.

Get the shortcut: https://polyhelper.ai/duo/

Free and open source (Apache-2.0): https://github.com/vadimchernets/c1m-duo

Android: the same pair inside the free Poly A1 app.

Made by Vadym Chernets, independent AI researcher (PhD); two of my posters on AI evaluation and verification are at NeurIPS 2026 workshops.