v1.0.0-beta.229 spec/v0.3.0
microsoft/agent-host-protocolJun 5, 2026 → Jun 6, 20261 day between releases
What's New
Older notes cover billing, not this spec; newer 0.3.0 adds MCP customizations and breaking renames.
Breaking Changes
- ToolCallBase.toolClientId is replaced by a discriminated ToolCallBase.contributor union.
- ChangesetSummary is renamed to Changeset.
- The changesets field moves from SessionSummary to SessionState.
- UserMessage is renamed to Message and gains an origin field.
New Features
- MCP servers are modeled as first-class McpServerCustomization entries with lifecycle states, an optional mcp:// channel, and an optional mcpApp block.
- A new session/mcpServerStateChanged action provides narrow upserts of state and channel for high-frequency transitions.
- MCP Apps support arrives via AhpMcpUiHostCapabilities plus an optional InitializeParams.capabilities client bag.
- ChangesetOperation gains status and error fields.
- A changeKind field is added for session, branch, turn, and similar entities.
Improvements
- The contributor union enables clean attribution of tool calls to either the client or an MCP server.
- McpServerAuthRequiredState now carries ProtectedResourceMetadata along with reason, requiredScopes, and description.
- Customization now includes McpServerCustomization at the top level so hosts can surface globally configured MCP servers.
Upgrade Notes
Migrate toolClientId usages to the new contributor union and rename ChangesetSummary to Changeset throughout. Move changesets reads and writes from SessionSummary to SessionState, and update UserMessage to Message with origin. Bump the spec version to 0.3.0 and regenerate any SDKs or clients.
The Two Releases
v1.0.0-beta.229
Jun 5, 2026· 5 months ago
A beta release focusing on billing and taxation capabilities, including tax codes, tax behavior in ledgers, and a promotional credit purchase state machine, along with SDK generation updates.
Full release notesAHP Spec v0.3.0
Jun 6, 2026· 5 months ago
Core protocol update regarding MCP servers as first-class customizations and tool attribution.
Full release notes