Passkey-Based Passwordless Logins Were Integrated into the X iPhone App
Passkey log-ins for iPhones and iPads are now supported by X, giving members access to the security feature irrespective of their "Premium" membership.
By creating a passkey for X, users can depend only on the security of their device—whether it be Face ID, Touch ID, or your device's passcode—instead of typing a password every time they log in to their accounts.
Passkeys are now only accessible in the US, and X has not said when it will make the login feature available for desktop computers, Android devices, or other nations.
Don't worry if the functionality hasn't appeared yet; X's passkey deployment doesn't appear to be completed yet (some users reported still not having access as of Tuesday night on the East Coast).
X iPhone app added passwordless logins with passkeys
Passkeys function as an extremely secure "remember this device" system by creating two cryptographic keys, one of which is kept locally and the other on X.
This ties the security of your account to the security of your device.
In addition to Google, Microsoft, PayPal, Nintendo, etc, X is the most recent to implement passkey technology.