Twitter/X

Mastra launched a feature called Harness (announced by Sam Bhagwat @calcsam on…

2026-06-18 · 21:32 UTC ·@Kazanjy ·0 min read

Brief

Mastra's new Harness feature creates a Session with plan/build modes to orchestrate agent workflows: lifecycle management, spawning/forking subagents, per-call or per-session tool approvals, user prompts, and queue/steer controls. It ships with skills, a sandbox, browser access, a heartbeat, and channel support (notably Video), per Sam Bhagwat (@calcsam).

Why it matters

Mastra launched a feature called Harness (announced by Sam Bhagwat @calcsam on 2026-06-18) that provides a Session with distinct plan and build modes.

Key details

  • Harness supports managing thread lifecycle, spawning or forking subagents, approving tools either per-call or per-session, asking users questions, and queueing/steering execution.
  • Harness includes integrations for skills, a sandbox, a browser, a heartbeat mechanism, and channels including Video.
Source evidence

Mastra just keeps adding more and more amazing functionality.

Sam Bhagwat (@calcsam)

Today we're launching @mastra Harness

Harness gives you a Session with plan/build modes.

It lets you manage thread lifecycle, spawn or fork subagents, approve tools per-call or session, ask user questions, queue/steer.

With skills, sandbox, browser, heartbeat. channels:

Video

— https://nitter.net/calcsam/status/2067634651062296859#m