First official release or announcement for each extension milestone
| Date | Platform | Extension Type | Milestone |
|---|---|---|---|
| Jun 2023 | OpenAI | 🔧 Function Calling | GPT-3.5/4 API gets structured tool use |
| Nov 2023 | OpenAI | 🤖 Custom GPTs | No-code GPT builder announced at DevDay |
| Jan 2024 | OpenAI | 🏪 GPT Store | Public marketplace for custom GPT distribution launches |
| Nov 2024 | Anthropic | 🔧 MCP Standard | Model Context Protocol announced as an open integration standard |
| Feb 2025 | Anthropic | ⚡ Commands | Claude Code research preview launches with CLI commands |
| May 2025 | Anthropic | ⚡ Commands (GA) | Claude Code generally available with Claude 4 |
| Jun 2025 | OpenAI | 🔧 MCP Connectors | Custom connectors launch in ChatGPT deep research for Enterprise/Edu |
| Jun 2025 | Anthropic | 🛡️ Hooks | Claude Code hooks released (v1.0.38) |
| Oct 2025 | Anthropic | 🧠 Skills | Agent Skills announced for Claude Code; SKILL.md-based skills supported in Claude Code 1.0+ |
| Oct 2025 | Anthropic | 📦 Plugins | Claude Code plugins announced |
| Feb 2026 | OpenAI | 🧠 Skills | Codex v0.94.0 adds `.agents/skills` loading for `SKILL.md`-based custom skills; v0.95.0 adds personal skills |
| Mar 2026 | OpenAI | 📦 Plugins | Codex CLI plugin system lands in v0.110.0 |