The I2C fast mode defines transfer rates up to 400 kbit/s whilst the first I2C specification dated 1982 had a limit of 100 kbit/s. To accomplish 400 kbit/s the timing requirements were defined more strictly.
In April 2006, NXP (formerly Philips) introduced Fast-mode Plus, allowing transfer rates up to 1 Mbit/s.
Additionally, there is the high speed mode running the bus at up to 3.4 Mbit/s.