Mastra core 1.79.0 moves agent sessions to session IDs

Mastra published @mastra/core 1.79.0 on October 21, 2026, according to the GitHub release from mastra-ai. The release makes agent controller sessions addressable by session ID, adds span-level aggregation for observability, and introduces experimental MCP Events.

Release facts

What changed

• Sessions use session IDs (breaking). The release notes say sessions are addressed by sessionId instead of resourceId + scope. Many sessions can share one resourceId, which now only identifies whose threads and memory a session uses. controller.getSession(sessionId) is added, getSessionByResource is removed, and deleteSession() takes { sessionId }. If id is omitted it defaults to the resourceId, so one-session-per-resource code keeps working.
• Session takeover guard. createSession throws when an explicit resourceId doesn't match the live session with that id.
• Span aggregation. Storage adapters can implement aggregateSpans() and advertise the span-aggregate feature, for questions such as p95 latency per tool or token spend per calling agent. Grouping by model or provider is not supported yet.
• Trace queries. aggregateTraces() can group by root span entityId. Observability queries also gain timeToFirstChunkMs fields.
• Experimental MCP Events. MCP servers can publish event streams that clients poll, hold a stream open for, or receive via signed webhooks, with Studio inspection under mastra dev.
• Sandbox filesystem and Connect. WorkspaceSandbox can expose an optional filesystem for one-roundtrip file operations. @mastra/connect adds per-end-user connection scoping and a Microsoft Teams channel.

Other breaking changes listed: the thread-row query contract uses timeRange.traces / timeRange.threads, querySpans() drops model/provider filters and several response fields, and channel resolveResourceId / resolveThreadId contexts now require requestContext.

Questions

Will existing session code break? The release notes mark the change as breaking. Code that relied on scope or getSessionByResource must move to session IDs, though code with one session per resource keeps working because id defaults to resourceId.

Do I need new storage adapters for the observability changes? The release notes say the querySpans() contract change requires updated storage adapters, and adapters without the span-aggregate feature reject aggregateSpans() as not implemented.

Is MCP Events stable? No. The release notes call it experimental and based on the SEP-3415 draft.

For more, see the Mastra hub, the Frameworks category, and the earlier Mastra Core 1.78 launch.