Phase Build

Chris Williams places Build as P4 in the eight-phase ADLC cycle described in "Two Human Gates and Everything Between Is Machine-Checked" (12 June 2026): one agent per ticket, running on «modèles mid-tier par défaut», with two-strike regeneration, meaning an agent that stalls is killed and restarted fresh rather than nursed along. Williams rejects personas here; capabilities come from context, tools and the charter. The phase sits at the light middle of what he calls a barbell distribution of effort, heavy at both ends (plan in P1, prove in P5), light where the code actually gets written. That inverts the classic agile economics in which building badly is what costs money.

The second appearance is different in kind. Bret Taylor's redesign of Sierra's engineering interview, published 20 April 2026, names its middle onsite stage "Build": the evaluator leaves the room and the candidate has two hours to bring their own idea to life, with whatever AI tools and frameworks they choose, free to pivot or cut scope. What follows is a Review stage where evaluators examine the code, debate product choices and ask how the AI was used.

The same word covers two hours of unsupervised human construction and a machine-executed ticket run bounded by frozen tests. Both are unattended by design, and both push the human judgment to the phases on either side. Neither Williams nor Taylor treats the act of building as the place where the difficult decisions get made.