I'm not party to the detail (so none of this is confirmed) - but broadly the policy in London has already moved towards safe, segregated cycle lanes.
So, expect to see many more, probably including some longer eye-catching ones.
There will also be more focus and money spent on junctions.
The buzzword will be "step-change".
Aside from the infrastructure - which cyclists will no doubt judge when it is delivered - this is also a big day and a victory for London's cycling bloggers.
These sites - among others - started campaigning for improvements to cycling safety in the years before the last Mayoral election. They were a thorn in the side of the Boris Johnson administration:
Their voices - and the message - got louder after a number of deaths, particularly around Bow roundabout.
They also began to shift the policy of more traditional organisations like the London Cycling Campaign, which in turn became more aggressive in its demands.
They were also helped by the campaign at The Times just prior to the last Mayoral Election.
Then the cycling lobby - usually a split and disconnected group - managed to get all the candidates to commit to improvements to cycling safety.
To give the Johnson administration credit, they have since engaged with the lobby, including some of the bloggers.
And now some of these internet campaigners have become involved and had direct input into an announcement set to be made tomorrow.
The cycling commissioner himself, Andrew Gilligan, has written and blogged about cycling for some time.
He has been critical of Transport for London and Cycling Superhighways on a few occasions.
The headlines tomorrow will probably be about the practicalities of the new infrastructure.
But what it will also show is the power of bloggers in mobilising opinion and changing the political landscape.
Tomorrow we will see the mayor outline his vision for cycling over the next 10 years.
Is this the first transport policy moulded by bloggers?