From Idea to 100 Million Users
Earlier this year, a small team of Meta engineers began pursuing an ambitious idea: a text-based conversation app that would also be interoperable with other social platforms. The goal was to build a decentralized (or federated) app where content posted on one platform could be viewed from others—and vice versa.
On July 5, Instagram users were surprised with an invitation to try Threads. Within five days, the app surpassed 100 million sign-ups, marking the most successful app launch ever. The deployment was driven by a compact engineering group working alongside Meta's infrastructure teams, taking the product from conception to massive scale with virtually no downtime.
Building Fast With Existing Infrastructure
Threads was developed in a startup-like environment. A small, high-trust engineering group worked with close alignment to leadership, including Instagram head Adam Mosseri. The team grew to roughly 60 engineers over several months, coordinating through daily burndown syncs and monthly milestones.
The engineering staff intentionally used Instagram's Python backend whenever possible. This didn't just save time—it also let them reuse data models, business logic, and security protocols. Perhaps most usefully, it allowed users to sign in using their existing Instagram accounts, simplifying the onboarding process. The mobile apps themselves were settled on Swift for iOS and Jetpack Compose for Android.
Given the stringent timeline, the team narrowed the feature set to essentials. Keyword search, private messaging, and the decentralized elements were deferred in favor of functionality the team could realistically deliver. Infra engineers pulled experience from Meta's large-scale systems to scale up as demand surged.
Launching Early, and Scaling Fast
When an opportunity to release early emerged, the team seized it. This meant the product reached users while anticipation was high, but left less time for dark testing and config adjustments in distribution channels.
On launch day, dedicated rooms were set up across San Francisco, Menlo Park, New York, and London. Engineers from infrastructure, product, and on-call teams all collaborated, using internal monitoring tools like ODS and Scuba to track key metrics and issue health checks in real time.
Although some engineers had never managed a launch of this size, the production engineers treated it as routine and provided critical coordination to ensure the rollout stayed smooth.
The Fediverse Is the Future
Shortly after its debut, Threads took a step toward open standards by letting users verify their profiles on ActivityPub-supported platforms like Mastodon. The notion of a federated universe is less familiar to the general public, but the design goal is comparable to email, where SMTP enables messages to flow seamlessly between services like Gmail and Yahoo Mail.
Social platforms today don't work that way—an Instagram user cannot follow someone on Tumblr, for instance. Implementing ActivityPub for Threads would open the door to interoperable social content properties, benefiting millions of users. This would involve letting users distribute posts to federated servers or consume content from creators on other applications, delivering more control over online presence.
Iterating With Speed
Having shipped publicly, the Threads team has since returned to feature development, reaching parity with user expectations. Web support arrived, despite early limitations. In the weeks that followed, additional upgrades appeared, including a Following feed, editorial controls for alt-text, and the ability to share threads directly to Instagram DMs.
The rollout of keyword search is significant, marking the ability to find specific topics. Marking a milestone announcement, this feature just became more accessible, initially launching in English and Spanish on mobile and web in Argentina, India, Mexico, the UK, and the US.
The technical work on Threads was completed within five months due to the freedom the team was given to run experiments and iterate quickly. Early prototypes were tested and discarded liberally. The activity feed alone was rewritten three times before settling on a final approach. “Code wins arguments” was the guiding principle behind rapid refinement cycles.
The hope is that Threads will become a central destination for viral conversations, cultural commentary, and creator interactions—built by using Meta’s infrastructure and persistence to move quickly and build what matters.
