Parallel Agents & Ruby’s New Toys: Copilot’s Canvas and Ruby 4.0’s ZJIT + Ruby Box
Two hands-on experiments. First, click through a live simulation of GitHub Copilot’s new multi-agent Canvas running four unrelated tasks at once on separate branches. Then step into Ruby 4.0’s two most-slept-on additions — the ZJIT compiler and Ruby Box isolation — and see exactly what they change.
Run four Copilot agents in parallel, on four branches
GitHub’s new Copilot app introduces “Canvases” — shared surfaces where multiple agents work simultaneously without colliding, each on its own branch. Launch the board below and watch four unrelated tasks progress independently. Click any card to expand its live log.
Sources: GitHub Blog — Copilot App · Microsoft Community Hub — Canvas as a runtime · Digital Applied — orchestrating many agents
Ruby 4.0 shipped two features most teams haven’t touched yet
Released December 25, 2025, Ruby 4.0 brought a brand-new JIT compiler (ZJIT) alongside the mature YJIT, plus an experimental isolation model (Ruby Box). Pick one below.
Try either compiler with a single flag:
Bars are illustrative, built from ranges reported by Shopify’s Rails at Scale (ZJIT launch) and the official Ruby 4.0.0 release notes. ZJIT already beats the plain interpreter on most workloads but isn’t at YJIT parity yet — that’s explicitly the goal for Ruby 4.1.
Ruby Box confines classes, monkey-patches, and even loaded libraries to a specific box — so two versions of your app can run side by side (think blue-green deploys, or testing a risky patch without touching the main process). Flip the switch, then try patching each box.
With RUBY_BOX off, a patch applied in either box leaks into the other — same process, same global state. Flip the switch on and try again.
Which Ruby 4.0 feature should you pilot first?
Check what’s true for your team — see a live recommendation.
