otterlink
microvmvmmCognition's homegrown behind Devin, paired with a blockdiff snapshot format for fast fork/rollback.
documentedCognition Blockdiff blog post ↗
otterlink is Cognition's custom , the isolation primitive behind Devin's cloud Devbox VMs and the only closed coding-agent that names its primitive. Each Devin session gets its own guest kernel behind a hardware boundary; Cognition argues VM-level isolation beats containers because containerized agents share a kernel. It is paired with blockdiff, a custom block-level VM-disk snapshot format enabling fast fork and rollback (reported ~10x faster VM startup and ~200x faster snapshots versus EC2). is deliberately open by default.
Strengths
- Own guest kernel per session, a hardware boundary, not a shared-kernel container
- blockdiff snapshots give fast fork/rollback (reported ~200x faster than EC2)
- The best-documented custom primitive among closed coding agents
Limitations
- Proprietary to Cognition, not available as a standalone tool
- Egress is open by default (Cognition's deliberate choice)
- Cloud-only; self-hosting is a dedicated single-tenant VPC, not the hypervisor