v0.8.2 spec/v0.5.0
microsoft/agent-host-protocolJun 26, 2026 → Jun 26, 20261 day between releases
What's New
AHP 0.5.0 introduces multi-client sessions and progress tracking with breaking protocol changes.
Breaking Changes
- Renamed `session/activeClientChanged` to `session/activeClientSet`.
- Removed `session/activeClientToolsChanged`.
- `ConfigPropertySchema.enum` now accepts `JsonPrimitive[]` instead of `string[]`.
- `ModelSelection.config` values now use `JsonPrimitive` instead of string-only values.
- Session state is flattened and now exposes `activeClients`, so consumers must adapt to the new shape.
New Features
- Multi-client session support via `SessionState.activeClients`.
- Generic `root/progress` notifications correlated by `progressToken`.
- `chat/activityChanged` action for updating a chat's current activity.
- Optional `createSession.progressToken` plus model token-limit fields on `SessionModelInfo`.
- `SessionSummary._meta` presentation hints and `session/activeClientRemoved` action.
Improvements
- Flattened session state simplifies the session model.
- Progress notifications let hosts report long-running work instead of silent hangs.
- `JsonPrimitive` alias broadens enum and config value support to numbers, booleans, and null.
- `activeClientRemoved` enables releasing individual clients without disturbing others.
- Optional session metadata supports lightweight session-list presentation.
Upgrade Notes
Update clients to use `session/activeClientSet`, stop relying on `session/activeClientToolsChanged`, and migrate enum/config values to `JsonPrimitive`. Consumers must read the flattened session state and `activeClients` array, and can opt into `root/progress` via `createSession.progressToken`.
The Two Releases
v0.8.2
Jun 26, 2026· 4 months ago
This release introduces A2A agent discovery, richer skills capabilities, and significant security hardening. It also introduces a durable run/task control plane and expands channel surfaces.
Full release notesAHP Spec v0.5.0
Jun 26, 2026· 4 months ago
Defines the protocol spec for AHP 0.5.0, establishing multi-client sessions, progress tracking, and the new `SessionState` structure.
Full release notes