Comment by Kinrany

> I'd just stress that at least for the Android client it's open source with some degree of quoting: the real git history is not shared (each release typically consists of a single huge commit), and the source is often published weeks after a release of the official client.

One thing I don't know is whether these delayed source releases are enough to validate releases published to app stores. If they are, this means Telegram is building up reputation and would have to burn it to publish a release with a backdoor not present in the source.

The other thing this allows is for a third party to maintain a fork without having too much trouble keeping up with new features.