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spec/v0.5.0 clients/go/v0.5.0

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microsoft/agent-host-protocolJun 26, 2026 → Jun 26, 20260 days between releases

What's New

Go client v0.5.0 implements AHP 0.5.0, flattening SessionState and reworking active-client and config types.

Breaking Changes

  • SessionState no longer embeds a Summary sub-struct; metadata fields are inlined and Model, Agent, CreatedAt, and ModifiedAt are removed from SessionState.
  • SessionState.ActiveClient is replaced by an ActiveClients slice.
  • SessionActiveClientChangedAction is renamed to SessionActiveClientSetAction.
  • ConfigPropertySchema.Enum now uses []json.RawMessage instead of []string.
  • ModelSelection.Config now uses json.RawMessage instead of a string-typed value.

New Features

  • ChatDraftChangedAction and ChatState.Draft sync a chat's in-progress input without touching ModifiedAt.
  • Message.Model and Message.Agent record the model/agent selection a message was composed with.
  • ChatActivityChangedAction updates a chat's activity description independently of the session summary.
  • ProgressParams (root/progress) plus CreateSessionParams.ProgressToken enable generic, token-correlated progress reporting.
  • SessionModelInfo token-limit fields and SessionSummary.Meta presentation hints, plus a SessionActiveClientRemovedAction for releasing a single client.

Improvements

  • The Go module now tracks the AHP 0.5.0 spec, including multi-client sessions and generic progress notifications.
  • Session metadata is inlined for simpler, flatter access in Go code.
  • Enum and model-config values are carried as raw JSON, allowing numeric, boolean, and null values.
  • Long-running bring-up work (e.g. lazy SDK download) can be surfaced to clients instead of appearing to hang.

Upgrade Notes

Update all code that reads SessionState.Model, Agent, CreatedAt, or ModifiedAt, since those fields no longer live on SessionState. Replace ActiveClient usage with ActiveClients, rename the active-client-changed action type, and adapt enum/config handling to json.RawMessage. Regenerate or hand-edit serialization code to match the flattened wire shape.

The Two Releases

spec/v0.5.0

AHP 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
clients/go/v0.5.0

Go module v0.5.0

Jun 26, 2026· 4 months ago

Implements AHP 0.5.0 for the Go module, flattening SessionState and adding active client management.

Full release notes