Keybase is not softer than TOFU

As a result, Keybase uses a key hierarchy so that by transferring 32 bytes of secret data from the old device to the new, the new device can see all long-lived cryptographic data (see the FAQ below for more details). In our early days (2014 and early 2015), Keybase was a web-based PGP app, and since there were few better options, we had a feature for users to store their PGP private keys on our servers, encrypted with their passphrases (which Keybase didn’t know). She encrypts the secret half of the PUK for new device’s public key, and the new device pulls this ciphertext down via the server.

Source: keybase.io