Layer 9 · Applications & Interfaces

Where people meet AI: chat assistants, copilots inside existing tools, and specialised apps.

In simple words: The apps where people meet AI: chat apps, voice helpers, and AI buttons inside the tools they already use.

reviewed 2026-10-30

Like: A shopfront: customers see the counter and the product, not the warehouse and supply chain behind it.
Where it breaks: A shop sells the same product every time. AI apps produce different output each time, so interfaces must handle uncertainty, errors and human review.

Key players

What it means for your business: Your customers already use general assistants, so decide what your product does that they cannot, and whether to build AI features yourself or plug into these assistants.

• ChatGPT: OpenAI's assistant; by far the largest consumer AI product.
• Gemini: Google's assistant, the clear number two behind ChatGPT.
• Microsoft 365 Copilot: Assistant built into Word, Excel, PowerPoint, Outlook and Teams.
• Claude: Anthropic's assistant; with fast-growing paid use in 2026.
• Doubao: ByteDance's assistant, heavily used in China.
• Perplexity: Answer engine that searches the web and cites sources; also a browser.
• Cursor: AI-first code editor, in the top 50 AI web products.

As of 2026-10-15. Sources: The Top 100 Gen AI Consumer Apps, 6th edition (a16z) (2026-03-09); Microsoft 365 Copilot (2026)

What it gives the layer above

Value to people, plus usage and feedback that flow back down the stack.

What it needs from the layer below

Agents or orchestrated model calls from the layers below.

Concepts

• Chat assistants
  General-purpose chat apps where you type, talk or upload files, and an assistant answers, writes, searches and uses tools.
• Voice & multimodal interfaces
  Talking to AI out loud and showing it images or video, through phones, cars, speakers and glasses.
• AI features inside products
  AI built into ordinary apps as buttons and features, where the app's own server calls a model API behind the scenes.
• Copilots
  AI built into the tools people already work in, such as code editors, documents and email, suggesting and increasingly acting while the person stays in charge.

Walkthrough

1. Monday starts in a chat app. Sam asks a chat assistant to plan the week. It searches the web and books a table using a browser agent.
2. Hands busy, so Sam talks. While cooking, Sam asks out loud and shows the phone camera the fridge. Speech and images go in; a spoken reply comes back.
3. AI hidden inside an app. At work, the expenses app has a “summarise receipts” button. Behind it, the app's server calls a model with Sam's own data.
4. A copilot in the editor. In the code editor, a copilot suggests changes and, in agent mode, fixes a bug while Sam reviews the diff.

Examples

• Chat assistants (ChatGPT, Claude, Gemini)
• Coding copilots (GitHub Copilot, Cursor)
• Voice assistants and smart glasses
• AI features inside everyday apps
• Vertical apps (legal, health, support)