The star of Steven Moffat and Mark Gatiss’ detective series told BBC Radio Wales: “It's going to be full of surprises for you, and for us and for everybody. I think we just know to expect the unexpected now.”
He added: “The plans they have got for the overarching series - oh man, it's just so exciting!“
Freeman also expressed his “delight” at winning (albeit in absentia) Outstanding Supporting Actor in a Miniseries or Movie at the 66th annual Primetime Emmy Awards over the weekend.
He explained that he had learned of his success through a text from his American agent.
Sherlock scooped three Emmys overall, with Benedict Cumberbatch and Steven Moffat also honoured with awards.
Best moments from Sherlock
Best moments from Sherlock
1/9 Best Sherlock moments
Sherlock's 'dies' after he falls off the edge of St Bart's hospital. The nation mourned for all of five minutes before it was revealed that the super sleuth had faked his death
2/9 Best Sherlock moments
Sherlock and Moriarty go in for a kiss - prompting shipping theories to crop up across the internet.
3/9 Best Sherlock moments
Sherlock accidentally disrobes in Buckingham Palace in 'Scandal of Belgravia'.
4/9 Best Sherlock moments
Sherlock and Watson play a drinking game during Watson's two-man stag do. The rest of the evening ends in typcically raucous style.
5/9 Best Sherlock moments
Sherlock and Watson have a punch up in 'The Empty Hearse'. In possible the best fight since 'Bridget Jones's Diary', the pair tussled furiously when Sherlock surprised Watson by coming back from the dead.
6/9 Best Sherlock moments
Molly and Sherlock's Christmas present was one of the sweetest moments between the pair. The romance that viewers want to happen.
7/9 Best Sherlock moments
Sherlock exposes Sun journalist Kitty Riley, who pretends to be a big Sherlock fan.
8/9 Best Sherlock moments
The series one finale of 'Sherlock' left fans on tenterhooks after Moriarty strapped a bomb to Watson in a standoff with the detective
9/9 Best Sherlock moments
It was a partnership made in heaven - Sherlock and Watson meet for the first time.
"It keeps going from strength to strength really. We're all very proud of it; we're all very pleased to be in it,” Freeman said.
“I think, as a nation, it's one of the UK's finest exports.”
Fans had already been teased about the forthcoming 2015 series at the Los Angeles ceremony, as Moffat and Gatiss promised “darker” new epsiodes.
Season four of Sherlock will reach UK screens late next year as a one-off special and new three-part run.
The exact air dates are yet to be confirmed but Moffat insists that “when they go out is up to the BBC”.
“I am their loyal servant, I simply do what they ask me,” he joked.Reuse content