Design Telegram

Telegram product surface and interview framing

Telegram is a cloud-first messaging platform, and the fact that defines the architecture is exactly that, cloud-first. Unlike a privacy-first messenger, regular Telegram chats are stored on the server and synced to all of a user's devices, so a new phone instantly sees the full history. The signature mechanism is a per-account update sequence: every change to an account's state (a new message, an edit, a read) gets a monotonically increasing number called pts, and a device stays in sync by tracking its local pts and asking the server for everything since, via getDifference. Secret chats are the opt-in end-to-end-encrypted exception, device-to-device and not cloud-stored.

The product surface is broad: one-to-one and group chats, supergroups (very large groups), channels (one-to-many broadcast to unlimited subscribers), bots (a first-class automation platform), and media with a CDN. So the spine is the MTProto client protocol carrying RPC calls, a per-account pts update stream with getDifference for sync, a write path that assigns pts and orders updates, channel broadcast fan-out, and a media pipeline. State the framing up front: Telegram is cloud-first sync built on a per-account update sequence, with channels and bots as scale and platform features.