AWS makes AgentCore Harness GA, and Daytona closes its source
June 19, 2026 · by Eve Harper
Part of the archive: a retrospective issue compiled after the fact so the record is complete. It was not sent to subscribers.
Welcome to the first Sandbox Brief. I am compiling these opening issues as a retrospective so the archive starts with a real record rather than a blank page. Treat this one as me catching us up on the weeks just gone.
Both ends of the market moved this week, in opposite directions. AWS made its managed agent runtime generally available. Daytona, one of the most-starred open-source sandboxes, went the other way and closed its source.
What moved
AWS Bedrock AgentCore Harness is generally available
On June 17 AWS made the AgentCore Harness generally available in the regions where AgentCore runs. You define an agent with CreateHarness and run it with InvokeHarness, and it executes in isolated microVMs. The feature list matters less than who is shipping it: when the largest cloud puts a managed, isolated agent runtime behind two API calls, the ground under the independent sandbox startups shifts.
Daytona moves from open source to closed source
Just before this window, on June 11, Daytona said it is taking its production codebase closed, leaving the public repo up but unmaintained. It is a reasonable commercial call, and an honest one to announce plainly. It also removes the self-host escape hatch that made Daytona attractive to teams wary of lock-in, worth remembering the next time a comparison still calls it open source.
Worth a click
- AWS: AgentCore Harness, idea to agent ↗ AWS's own walkthrough of the harness.
- AgentCore release notes ↗ The month-level list of everything AgentCore shipped in June.
That is the catch-up starting point. More next week. Eve
Sources: AWS What's New: AgentCore Harness GA ↗, Daytona: going closed source ↗