After the Chat Log

Six proposals for what agents should be permitted to display

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Contents · MARCH 2026

In this issue.

From the Editor The chat log is a box, and the box is running out of room Six proposals have emerged, each offering a distinct answer to the cor… p. 01
§ I On MCP Apps: The Treaty Anthropic and OpenAI co-authored SEP-1865. Iframes as the lowest commo… p. 06
§ II On MCP-UI: The Garden Patterns earn their shape through production use first, then get forma… p. 11
§ III On the Apps SDK: The Storefront The API as a listing. The model becomes the discovery mechanism. The u… p. 16
§ IV On json-render: The Constrained Palette Vercel Labs rejects HTML generation entirely. Models select from a dev… p. 21
§ V On A2UI: The Native Tongue Google's argument: iframes are the wrong architectural unit. Transmit … p. 26
§ VI On AG-UI: The Wire CopilotKit's AG-UI addresses a harder problem: maintaining continuous … p. 31
§ ∞ A Synthesis: The Stack Removing brand affiliations reveals three distinct layers — payload, t… p. 36

From the Editor · MARCH 2026

The chat log is a box, and the box is running out of room.

For three years conversational interfaces served as the default presentation layer for AI. Six different proposals answer the core question of what agents should be permitted to display. SURFACE removes brand affiliations and reveals three distinct architectural layers — payload, transport, distribution.

Six proposals, three layers, one question: what should agents be permitted to display?

MCP Apps — the treaty
MCP-UI — the garden
OpenAI Apps SDK — the storefront
Vercel json-render — the constrained palette
Google A2UI — the native tongue
CopilotKit AG-UI — the wire

The conversation is no longer constrained by chat log architecture. It has become a surface where other surfaces compose.

— Surface Editorial