Sentient OS: The AI Agent That Learns Your Life While You Sleep

Your AI assistant knows nothing about you until you tell it. Every chat starts at zero, and whatever context you give it evaporates when the window closes. Sentient OS — a new Mac app from a Y Combinator Fall 2026 startup — takes the opposite approach: it studies your notes, emails, messages, calendar, files, and screenshots overnight, and writes what it learns into a plain Markdown knowledge base it actually uses.

I broke down the full story on NeurAITool, including pricing, privacy trade-offs, and a complete pros/cons verdict: Sentient OS: The AI Agent That Learns Your Life Overnight. Here's the condensed version.

The Core Idea: Memory That Builds Itself

You connect the sources you choose — Apple Mail, Calendar, notes, messages, files, screenshots — and a local model reads through them, typically overnight. By morning, it has distilled what it found into a folder of plain Markdown files: people, projects, preferences, the texture of your life.

The part that makes this design stand out: the knowledge base is readable and editable. If it misunderstands something, you edit the file. If it learned something you would rather it forget, you delete it. Most AI memory systems are opaque; you can hand things to them but you can never inspect or correct them. Editable Markdown flips that.

Two Features That Use the Context

Sidekick is the computer-use agent. Click the notch and it takes over a task with its own on-screen mouse cursor, carrying it out across your apps and browsers — informed by the context it already has, so you skip the briefing. It is the same category as the browser-automation wave (I covered OpenAI's Chrome extension agent and Google's Gemini Agent), except Sidekick starts with a head start: it already knows your life.

Double Tap is the one most likely to win skeptics over. Double-tap the right Command key and it drafts a reply using your personal context and examples of your own writing. Nobody wants to sound like a chatbot in their own inbox; this is the feature where the personal context actually shows.

Proactive suggestions wait for your approval before acting. The honest caveat: Sidekick can perform actions without per-click approval once a task is underway, so review automation permissions before delegating anything sensitive.

Pricing: Free Window, With a Door on It

The app is free, and the official site advertises a limited launch offer: entering the code FINAL_1000 in the app keeps it free for life. That framing says the free tier is a limited window — if the app interests you, claim it early.

One caveat: if you plug in an external provider (ChatGPT, Claude, and the like), that provider's charges are separate. Version 2.6, released 27 October 2026, explicitly lets ChatGPT Free and Go users try Sidekick, with usage governed by your ChatGPT plan.

The Honest Privacy Story

"On-device AI" does marketing work in 2026, so here is the accurate version. The built-in model analyzes your selected sources on your Mac and writes the knowledge base there — that part is genuinely local, and the app is open source (AGPL-3.0, around 690 GitHub stars), so the claims are auditable rather than asserted. The built-in model runs on as little as 8 GB of RAM.

What is not strictly local: cloud features can receive context or screenshots if you enable them. The honest framing is local-first with opt-in cloud, not "never leaves your machine." If maximum privacy is the goal, stick to local models. Requirements: Apple silicon (M1 or newer), macOS 15.4 or later. Windows users get a waitlist, not a product.

Takeaways for Builders

1. Editable memory is the right pattern. A self-building knowledge base that the user can read, correct, and delete is more trustworthy — and more useful — than any black-box memory store. Steal this design.
2. Context is the moat. Agents that arrive with your context skip the briefing step entirely. The products that win the personal-agent category will be the ones that minimize how much the user has to explain.
3. Local-first is the expectation. On-device analysis plus opt-in cloud is becoming the default privacy posture users demand from personal AI. Plan for it.

The full NeurAITool breakdown has the complete FAQ, all the numbers, and the verdict: Sentient OS: The AI Agent That Learns Your Life Overnight.