For so many people I, Claudius is THE novel about the first years of the Roman Empire and so has conditioned our whole reception of Rome and the rule of the emperors - and how Robert Graves would have laughed if he could have predicted that! Written as a 'pot-boiler' because he needed the cash, Graves deliberately fashions a decadent, immoral and corrupt milieu that has now passed into historical fact.
As a translator of Suetonius and Tacitus, two of the major sources he uses for his fictions, Graves is completely aware that both men had political agendas of their own when they chose to portray Augustus, Tiberius, Caligula etc in the way he did. Livia hardly gets a mention, along with the other imperial women, and Suetonius' portrait of Claudius himself is far less avuncular than Graves'.
Having said that, both this and the sequel Claudius the God are excellent novels: but just don't automatically assume they're also history because they're not.