GitHub Ships Copilot SDK Agent Factories With Free Replay

GitHub shipped Copilot SDK v1.0.9-preview.1 on July 30 with Agent Factories, a JavaScript closure that spawns and coordinates subagents on command, per the release notes.

That closure gets primitives to spawn subagents, run work in parallel or in sequence, and report progress, called over reverse RPC. The one that matters: journaling. A resumed run replays already-finished subagent work instead of paying to redo it. The release notes call re-running that work the single most expensive part of long agent runs.

GitHub's prior preview added an agentStop lifecycle hook, letting applications intercept and block a subagent from stopping mid-task. Rust and Java variants of the SDK shipped alongside the JavaScript one. GitHub's July 30 changelog covers all three: Copilot CLI, the VS Code agents window, and Visual Studio's new Agent preview.

Agent Factories is the marketing name here. The journaling primitive is the part I'd actually copy. Anyone building on agent SDKs pays for repeated subagent work every time a long run gets interrupted and resumed. I've felt that cost firsthand on long runs. A runtime that journals finished work and skips re-paying for it changes the economics of long-running agents more than any single IDE surfacing it.