Absolutely huge news. Although if we're all honest, not TOTALLY surprising.
He's been here before with McLaren in 2013. I'd wager he's seeing a similar pattern with Mercedes, a previously successful team slowly falling further and further away from the competition, a lack of fire and energy at board level, and significant brain drain. He probably felt it was now or never to make the jump to fulfil his ambition to do what his hero Senna never had the chance to, end his career at Ferrari.
For Mercedes it's a PR nightmare and is a damning verdict on their future ambitions. Every race with Hamilton this year will be framed in terms of Ferrari, they'll be totally sidelined as a brand. So what do they do? Do they try and pay Hamilton to take a year off in 2024 to stop him taking the teams secrets to Ferrari and avoid the media circus? Have him drive a test mule all season and put 100% behind Russell? Or be professional and try and end their relationship on a high (is the relationship still intact)?
On the flip side, by all accounts Mercedes see Antonelli as their next star so expect him in the seat come 2025 if he delivers in F2 this year. I've heard whispers that the tide is somewhat out on Russell after he was put in his place by Hamilton last season.
Also a penny for Leclerc thoughts, it's a lose-lose really. Hamilton will be 40 by the time he races for Ferrari. A 40 year old hasn't won a Grand Prix since Nigel Mansell won in Australia in 1994! Leclerc will be in his prime, in HIS team vs a 40 year old in the twilight of his career, he HAS to win right?