Devin's New 'Fusion' Harness Pairs a Frontier Model with a Cheaper Sidekick to Cut Coding Costs Up to 39%

Cognition introduced Fusion, a dual-agent harness for Devin Desktop and CLI that runs a frontier lead model like Fable 5.1 alongside a cheaper sidekick like SWE-2, sharing only briefs and results instead of full context to cut costs up to 39% versus Claude Code or Codex alone.