Klaviyo's 'Dark Factory' Writes Its Own Specs and Builds Through the Weekend — and All 2,300 Employees Were Required to Reach 'L3' Agent Fluency by June

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Klaviyo co-CEO Andrew Bialecki described an internal system called the Dark Factory that takes a prompt, writes the spec, decomposes the problem into subsystems, writes the contractual API interfaces between them, then dispatches subagents against each piece — building through the weekend and interrupting only when requirements are ambiguous. Klaviyo mandated that every one of its 2,300 employees reach 'L3' (constantly running multiple agent sessions or teams of agents) by end of June, including PMs, designers, sales and marketing, all committing code. Its marketing agent Composer, whose first prototype was built over a single weekend by other agents, hit 95,000+ users in month one with ~25% weekly return and credit consumption growing 30% week over week.