The midfielder was reunited with the 42-year-old on Tuesday after completing a move from Barcelona, whom Guardiola led to three La Liga titles and two Champions League trophies between 2008 and 2012.
The fee could rise to €25 million (£21.7m), with the 22-year-old becoming the Bavarians' third signing of the summer after Mario Gotze and Jan Kirchhoff.
"We all know what a coach Guardiola is," Thiago told reporters. "I played in the youth team under him and I have not seen a comparable coach. He has always had a lot of trust in me and I have to thank him now.
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"It's a beautiful city, especially now in the summer, the city bubbling with enthusiasm for football. Bayern is a great club with a long and successful history.
"I'm ready for next week's friendly against Barcelona. I am excited to see my old team-mates. They are all fine fellows and have all wished me the same thing: 'Good luck, success and all the best.'"
The playmaker also spoke about his new shirt, which will display 'Thiago' along with the No.6, but the Spain international joked that it was easier than using his full name.
"[My] whole name just did not fit on the jersey [and], besides, I've just always been called Thiago," he smiled.
Club CEO Karl-Heinz Rummenigge also gave his take on Bayern's newest signing, for whom he has nothing but praise.
"He is a player that suits Bayern," the Roten chief enthused. "He will keep the quality level high and is someone that suits our philosophy of buying young and talented players, just like Gotze.
"It may be an advantage that he mastered Baca's system but this was not the reason for his signing."