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Choose the smallest model runtime while keeping application authority explicit.

2 min read Updated 2026-08-18 #ai#models#tools

Cloud provides a shared runtime for model-backed features.

Cloud owns one personal conversation model for every user. Core supplies the global /api/ai runtime, storage, streaming, approvals, files, Projects, Skills, personalization, and recovery. Assistant is the standard GUI for those chats; applications attach Cloud resources and publish Capabilities instead of owning another chat silo.

The application still owns the product behavior. It decides:

  • who may use the feature;
  • which domain data enters the model context;
  • which queries and actions it publishes as Capabilities;
  • how the result changes application state.

That ownership does not move into a prompt. Cloud can authenticate the caller, store a turn, validate schemas, and pause for approval, but only the application knows which domain data may be disclosed and which operation is allowed now.

Choose the smallest API

Need Start with
Open the personal agent with initial text, files, or Cloud resources POST /api/ai/conversations
One validated background result runAiStructured()
A reusable application query or action Capabilities
A local runtime-only model tool defineAiTool()
Conversation files, Projects, Skills, or user memory Files, Projects, Skills, and personalization
Shared chat components Chat interface

Do not create a chat when one structured call is enough. Do not create a custom tool when a stable app operation should be published once as a Capability for several consumers.

Keep the application boundary

Cloud resolves the current user before it starts a turn. A referenced resource, Capability name, or Assistant deep link grants no access. The owning application authenticates every Capability call and checks its current domain permissions.

Model credentials stay on the server. Browser code sees sanitized model metadata, not provider secrets.

Cloud records conversations and tool results. The application database remains the source of truth for domain data.

Treat model output as untrusted input. Validate it before a write and run the same authorization checks used by a normal request.

Start with AI resources and access for an application entry point. Read Chat runtime and streaming for the conversation lifecycle and Models and providers for deployment configuration.

Connect a coding agent

The Cloud skill provides compact working instructions. MCP supplies exact current documentation when details matter.

CLI command
bunx skills add https://docs.example.com

This command installs the working instructions published by this website in the selected coding agent.

For exact, current details, also connect the MCP server through one of the agent tabs.

Installation uses the open-source Vercel Skills CLI.

The skill and MCP complement each other: the skill describes workflows, while MCP supplies current documentation.