September 15, 2026

The September 15, 2026 release of Mastra brings several major architectural additions across core, editor, and server packages. A new Studio Workflow Builder backend introduces an editor-owned agent for authoring persisted workflows, accessed via new server endpoints (GET /editor/workflow-builder/settings and POST /editor/workflow-builder/stream) under the stored-workflows permission scope. The new @mastra/connect package allows Mastra Platform integration connections to function directly as agent tools via a platform connection proxy, managing credentials and token refreshes without exposing provider secrets to the app. Thread ownership reassignment is now supported through Memory.updateThreadResourceId(), POST /memory/threads/:threadId/transfer, and client-js MemoryThread.transfer(), complete with transactional SQL updates and vector migration support. Background tool execution now supports explicit dispositions ('foreground', 'deferred', 'awaited'), caller-scoped completion signals using createBackgroundWorkSignalProcessor(), and bounded delegated execution. WorkspaceSandbox and DockerSandbox have gained bulk upload support with POSIX modes and volume subpath mounts, alongside bulk notification status updates and experimental cross-agent signaling.

• Migrate any instances of subscribeQueuedMessages({ resourceId, threadId }, listener) to subscribeThreadEvents({ resourceId, threadId }, listener).
• Update calls from ArchilFilesystem.grep() to ArchilFilesystem.diskGrep() when using @mastra/archil.
• Optionally configure the workflowBuilder option in MastraEditor and ensure required stored-workflows:read and stored-workflows:write permissions are set if using persisted workflow authoring.