Skip to main content

​
Selecting Fusion

Run /fusion during a session to open the Fusion model picker. You can choose the lead model, its reasoning effort, and the sidekick, or toggle Fast Mode. You can switch away from Fusion to a specific model at any time with /model. Fusion pairs a frontier lead model with a cost-efficient sidekick model, so you get frontier-level intelligence at a lower cost. The lead model owns your task — it plans, reasons through the hard parts, and reviews the work — while the sidekick handles the mechanical implementation. You interact with a single Devin; the pairing happens behind the scenes.

​
How it works

When you select Fusion, two models work together on every session:
  • Lead: a frontier model that drives planning, design decisions, investigations, and correctness-critical work.
  • Sidekick: a smaller, more efficient model that executes the lead’s plan — writing code, running builds and tests, and verifying changes.
Because most routine work runs on the cheaper sidekick model, a Fusion session costs meaningfully less than running the frontier model alone — frontier intelligence, for cheaper.
Choose Fusion when you want top-tier quality on a complex task without paying frontier prices for every token.

​
Choosing a pairing

Fusion isn’t a single model — it’s a family of lead + sidekick pairings. In the model picker, select the Fusion family, then configure:
  • Lead: which frontier model drives the session.
  • Effort: how much compute the lead spends reasoning before responding.
  • Sidekick: which cost-efficient model executes the work. All leads show a recommended sidekick.
  • Fast Mode: swaps in faster variants of the same models where available — same intelligence, higher speed, at a higher cost.
Selecting fusion directly (for example /model fusion) opens the model picker.

​
Availability

Fusion is available on paid plans in Devin CLI 3000.10.20+ and Devin Desktop 3.10.0+. It’s not included in free or trial tiers.

​
Pricing

Fusion bills each model in the pairing at its own rate: the lead at its frontier rate and the sidekick at its lower rate. You can see both rates in the model picker.
Lead and sidekick tokens draw down your quota at each model’s own per-token rate.

​
Tips for getting the most out of Fusion

  • Start with Fable 5.1 + SWE-2. This is our recommended pairing for best results. Fusion’s instructions are tuned for how each pair works together, including how much detail the lead provides and what exploration it delegates.
  • Check your session’s usage. In Devin CLI, run /session-stats (or /stats) to see token usage, cost by model, and estimated Fusion savings when pricing data is available. Compare total cost and result quality across similar tasks rather than choosing models by token price alone.