MIUI has just rolled out new update for Mi3 but still based on 4.4.4 Kitkat. The MIUI version 6.5.1.0 can be update manually or via OTA (Over-The-Air) update.

OTA Update can be done by going to Setting – About Phone – System Updates – Check Now

Please take note the file size is at 376MB. Do update it when you are connected to WiFi environment to avoid extra charges on your data.

Beside that, you can update it manually by downloading the ROM and sideload it – link

Changelog:

ContactsNew – Support choosing content to send when sending contacts via SMS (03-10)
Fix – After importing a contact from SIM card, operating in that contact detail page might cause UI error (04-09)
Lockscreen, Status Bar, Notification BarNew – Lock screen password can contain only numbers (03-06)
New – Added icons superscripts, notifications ringtone/vibration, notification light options in notifications management page (04-07)
Optimization – Animation effect when pulling down the notification shade (03-12)
Optimization – ‘Prevent pocket dial’ option is disabled by default, and is moved to Lockscreen page (03-18)
Optimization – If using pattern lockscreen, tailing effect will only display when the pattern is made visible (04-01)
Optimization – Optimized prompt text for clicking to open lockscreen notifications (04-01)
Optimization – Adjusted errors prompt text when changing SIM card PIN code (04-01)
Optimization – Animation details of waking screen (04-01)
Optimization – Optimized ‘Skip swipe screen’ and ‘Prevent pocket dials’ settings options (04-09)
Optimization – New notifications will not wake screen when smartcover is closed (04-09)
Fix – Sometimes, lockscreen was transparent (03-04)
Fix – Settings FC caused by changing toggle position in Settings (03-04)
Fix – Black screen when switching system languages (03-10)
Fix – For dual-SIM devices, signal bar did not refresh when SIM card status changed (03-23)
Fix – Sometimes, status bar displayed ‘no Internet connection’ (03-25)
Fix – The roaming mark did not show in status bar when roamed to some network types (03-25)
Fix – Sometimes, pressing volume + button caused phone to reboot (04-01)
Fix – Changing system language caused system to crash (04-07)
Deletion – Removed ‘long press back button in lockscreen to launch camera’ option (03-18)
Home screenNew – Global search supports searching online content (03-19)
New – Global search supports webpage searching (03-23)
Optimization – Enhanced Recents page launching speed (03-25)
Optimization – Enabling one-handed mode for the first time will lead to one-handed mode settings page automatically (04-10)
Fix – Calculation accuracy problem in Calculator widget (03-02)
Fix – Sometimes apps could not be launched (03-04)
Fix – Lag in the Power button menu animations (03-10)
Fix – Sometimes Recents page was empty (03-17)
Fix – Sometimes, home screen icons were repeated (04-07)
Fix – Clock widget did not show (04-09)
WeatherFix – Swiping up/down was recognized as swiping left/right (04-08)
Fix – Some inconsistency in weather information (03-31)
Fix – Delay in date update after adding cities (03-31)
Fix – Using third party font caused temperature text to misalign (04-08)
Fix – Temperature text was misaligned when first launching Weather app (04-08)
EmailNew – Support adding embedded images when editing mail content (03-24)
New – Swipe left on an attachment in attachments manage page will enter the corresponding mail (03-24)
CalendarNew – Sync calendar to Mi Cloud (03-11)
Optimization – Launching speed of calendar widget after booting up the device (04-09)
Fix – Fixed the error that clicking “More” button might cause the action bar to fold automatically (02-26)
BlocklistNew – Support syncing blocklist and exceptions list (03-18)
New – Support customizing blocklist notifications (03-30)
Clock / CalculatorNew – Timer supports setting time over one hour (04-07)

Source: MIUI Forum