Official Guidebook[]
Official statements that Base Sonic is faster than light.
Pedigree Books (August 2013). "Profile: Sonic". Sonic the Hedgehog Super Interactive Annual 2014. Pedigree Publishers. p. 8. ISBN 978-1908152077. "Sonic runs faster than the speed of light and according to the Guinness Book of Records, he is officially the fastest video game character of all time!"
Statements (Conjecture)[]
Takashi Iizuka: "We aren't aware how fast Sonic the Hedgehog is. In some games, he is able to go beyond the light barrier. We don't really know, the best way we can say it rivals the famous comic book hero, The Flash."
Takashi Iizuka is the game director, game producer, game designer, level designer, scenario writer and currently the head of Sonic Team.
https://en.wikipedia.org/wiki/Takashi_Iizuka_(game_designer)
Sonic Unleashed[]
Audureau, William; Petronille, Marc (1 January 2013). The History of Sonic the Hedgehog. UDON Entertainment. ISBN 978-1926778563. "During the day, he was his usual self, able to run anywhere at the speed of light; but at night, he became a slow and savage "werehog", prone to giving his enemies violent smackdowns."
The SPD meter in Sonic Unleashed shows that Sonic's light-speed dash clocks in at 390 SPD. The fastest you can go in this game is when Sonic is about 3519 SPD . This means that Sonic can run up to over 9 faster than light in Sonic Unlashed.
This calculation was sent to Takuza Iizuka, and he agreed.
Sonic Colors[]
Outran a black hole for a period of time.
Sonic Colors DS[]
Sonic Team, Dimps (November 12, 2010). Sonic Colors. Nintendo DS. Sega. Area/Level: Asteroid Coaster. "Sonic: Too Easy! / Omega: Data 130% higher than previous entry. Suspected error... / Tails: Nice run, Sonic! / Omega: Impossible... At this rate, light speed will be exceeded. / Sonic: Light speed? That's small time. There's no challenge! / Omega: Does not compute..."