**Chat β Agents** happened when tools like Claude Code, Cowork, and browser-use agents let the model operate a computer instead of just answering questions. The model became a doer.
**Prompts β Skills** happened when Anthropic formalized the skill format: a folder containing a SKILL.md file (with a short YAML header and Markdown instructions), plus optional scripts and reference documents. *Progressive disclosure* is the key mechanic β roughly 100 tokens of name and description are always visible to the model; the full instructions load only when the skill is relevant; scripts load only on demand. This keeps context lean even when you have hundreds of skills installed.
**Integrations β MCP** happened when MCP went from an Anthropic side project (Nov 2024) to a cross-vendor standard with 1,000+ production servers by Q2 2026.