YabSigmaOS vs Atlas
SigmaOS is a Mac browser on WebKit that treats tabs like a to-do list, in workspaces down the side, with an AI assistant called Airis.
ChatGPT Atlas was OpenAI’s Chromium browser for the Mac, with ChatGPT beside every page and an agent mode. OpenAI shut it down on August 9, 2026, and points people to the ChatGPT desktop app and its Chrome extension.
The short answer
- if you want workspaces and tabs you mark done, on a Mac
- if you browse by keyboard, with single-key shortcuts
- if you prefer WebKit to Chromium and want spaces
- OpenAI shut Atlas down on August 9, 2026: it may not open, runs no agent tasks and gets no security updates
- if you miss Arc and want spaces, pins and folders kept, on a Mac
- if you already pay for Claude or ChatGPT and want it to work in your signed-in tabs
At a glance
SigmaOS and Atlas, with Yab beside them for a Mac.
| What | SigmaOS | ChatGPT Atlas | Yab |
|---|---|---|---|
| Made by | SigmaOS Inc. (London) | OpenAI | Serafim Korablev |
| Status | No release notes since February 2025 | Shut down August 9, 2026 | Updated |
| Runs on | Mac | Mac | Mac |
| Phone app | None; Mac only. iOS has been on its roadmap since 2021 | None; Atlas was Mac only and shut down on Aug 9, 2026 | Not yet |
| Price | Free; Personal Pro $20/month or Personal Max $30/month for more AI | Shut down; it was free, with agent mode on paid ChatGPT plans | Free; its AI runs on your own Claude or ChatGPT plan |
| AI | Chat about pages, on its own AI service | An agent that works in pages, on its own AI service | An agent that works in pages, on your Claude or ChatGPT plan |
| Driven by outside agents | No | No | MCP and a command line |
| Engine | WebKit | Chromium | WebKit |
| Tabs down the side | Yes | A setting | Yes |
| Spaces | Yes | Not stated | Yes |
| Split View | Yes | Not stated | Yes |
| Extensions | Chrome Web Store | Chrome Web Store | Chrome Web Store |
| Ad blocker | Built in | Not stated | Built in |
| Open source | No | No | No |
Checked October 9, 2026 on each maker’s own pages, linked under Sources. Prices are per month, in US dollars.
Where they differ
What separates them, area by area. Where one plainly has more, it says who; where it comes down to taste, it says so.
AIAtlas leads
Only Atlas has an agent that clicks, types and finishes tasks in your pages. Airis chats about the page you are on, sums it up, looks things up and translates; no agent. Atlas put ChatGPT beside every page, with optional browser memories and, on paid plans, an agent mode; it no longer works.
Tabs and windowsSigmaOS leads
SigmaOS has tabs down the side, spaces and Split View. Atlas has tabs down the side as a setting and folders in the sidebar.
PriceSigmaOS leads
SigmaOS: Free; Personal Pro $20/month or Personal Max $30/month for more AI. Atlas: Shut down; it was free, with agent mode on paid ChatGPT plans.
Where it runseven
Both run on Mac. On a Mac, SigmaOS needs macOS 12 or later and Atlas needs macOS 14.2 or later. SigmaOS has no phone app: Mac only. iOS has been on its roadmap since 2021. Atlas has no phone app: Atlas was Mac only and shut down on Aug 9, 2026.
Engine and extensionsa matter of taste
SigmaOS is built on WebKit, the engine Safari uses; Atlas on Chromium, as Chrome is. Both take extensions from the Chrome Web Store.
PrivacySigmaOS leads
SigmaOS has an ad blocker built in. SigmaOS keeps history and cookies on your Mac unless you turn on sync, stored encrypted on AWS; its privacy policy doesn’t say where Airis requests go. Atlas has no ad blocker of its own. Atlas summed up pages for browser memories and deleted the originals; training on browsing was off by default.
UpdatesSigmaOS leads
SigmaOS: Still downloadable, with no public release notes since version 1.19 in February 2025. Atlas: OpenAI shut Atlas down on August 9, 2026: it may not open, runs no agent tasks and gets no security updates.
What their pages don’t lead with
Real limits, from the makers’ own words and our own use.
SigmaOS
- Mac only
- No public release notes since version 1.19 in February 2025
- Chrome extensions only partly work, behind its WebKit+ option
- Its AI is an assistant, and regular use needs the $20 or $30 plans
ChatGPT Atlas
- Shut down on August 9, 2026, with no more security updates
- Was Mac only, on Apple silicon
- Bookmarks, tabs and history had to be exported by hand
- Agent mode needed a paid ChatGPT plan
Yab, honestly
- Mac only: macOS 15.4 or later, no Windows, iPhone or Android
- New: first released in September 2026
- Its AI needs a Claude or ChatGPT plan; ChatGPT’s free plan may work with low limits
- WebKit, as in Safari: a site tested only in Chrome can misbehave
- Closed source
What changed lately
- August 9, 2026Atlas: Atlas shut down
- July 9, 2026Atlas: OpenAI said it will sunset Atlas for the new ChatGPT desktop app
- October 21, 2025Atlas: Launched for macOS
- February 4, 2025SigmaOS: Version 1.19.0, a performance update, the last release with public notes
Questions
Is SigmaOS free?
Yes, with limits on its AI. Free; Personal Pro $20/month or Personal Max $30/month for more AI.
Is ChatGPT Atlas free?
It no longer works. Shut down; it was free, with agent mode on paid ChatGPT plans.
Which has an AI agent, SigmaOS or Atlas?
Atlas. Airis chats about the page you are on, sums it up, looks things up and translates; no agent. Atlas put ChatGPT beside every page, with optional browser memories and, on paid plans, an agent mode; it no longer works.
Which runs on Windows, SigmaOS or Atlas?
Neither. SigmaOS runs on Mac; Atlas on Mac.
Do SigmaOS and Atlas have phone apps?
SigmaOS has no phone app: Mac only. iOS has been on its roadmap since 2021. Atlas has no phone app: Atlas was Mac only and shut down on Aug 9, 2026.
Is SigmaOS still being updated?
Still downloadable, with no public release notes since version 1.19 in February 2025.
Is ChatGPT Atlas shut down?
OpenAI shut Atlas down on August 9, 2026: it may not open, runs no agent tasks and gets no security updates.
Is there a third option on a Mac?
Yab, Yet Another Browser, is free for the Mac: tabs down the side with spaces, folders and Split View, as in SigmaOS; an agent in your signed-in tabs like Atlas’s, on the Claude or ChatGPT plan you already pay for. Claude Code, Codex and any MCP client can drive it too. It runs on WebKit, the engine Safari uses, and takes Chrome extensions. It is Mac only, and new.
More comparisons
- SigmaOS home page
- SigmaOS upgrade (plans)
- SigmaOS download (macOS only)
- SigmaOS update feed (appcast)
- SigmaOS 1.19.0 update notes
- SigmaOS 1.17.0 update notes (password manager)
- SigmaOS common questions
- SigmaOS docs: ad blockers and WebKit+
- SigmaOS docs: migrating from Arc
- SigmaOS privacy policy
- TechCrunch: SigmaOS turns to AI features for monetization (2024-03-26)
- Launch HN (Aug 16, 2021): founder says iOS and iPadOS are on the roadmap
- OpenAI help: Evolving Atlas into ChatGPT (retirement notice)
- OpenAI help: Atlas release notes (vertical tabs, tab groups, imports, profiles)
- OpenAI help: Getting started with Atlas (macOS 14.2, Apple silicon)
- OpenAI help: Setting up Atlas (imports, password manager)
- OpenAI help: Atlas data controls and privacy
- 9to5Mac: OpenAI is discontinuing Atlas (Jul 9, 2026, James Sun quote)
- 9to5Mac: what happens when Atlas shuts down (Aug 4, 2026)
- TechRepublic: Atlas shuts down Aug 9
- TechCrunch: Atlas launch (Oct 21, 2025)
- Wikipedia: ChatGPT Atlas (Chromium, timeline)
- OpenAI Help: ChatGPT Atlas retirement
- OpenAI Help: ChatGPT release notes (Jul 9, 2026 deprecation entry)
- TechRadar: Atlas for macOS, Windows, iOS and Android ’coming soon’ (Oct 2025)
- Yab Manual: Bringing in from another browser
- Yab Manual: Connecting Claude or ChatGPT
- Yab Manual: Extensions
- Yab Manual: Yab’s tools over MCP
- Yab Manual: Privacy
Yab, Yet Another Browser.
Free for the Mac. Arc’s sidebar, your own Claude or ChatGPT as the agent, Chrome extensions on WebKit.