It will have a mechanism that adjusts the cap so that it is at least 5% lower than the market rate.
This was lower than expected.
The current Brent-Urals spread is about at the cap currently. Russia's breakeven price is lower than this, so it is unlikely to reduce Russian oil output. But the goal isn't to stop Russian oil production, just reduce the oil profits.
Ultimately the goal here is to increase the bargaining power for Russia's current buyers like India and China. They have managed to secure $20-30 discounts off of the market price, and this cap should allow them to continue receiving steep discounts.
This is especially the case if the price of oil spikes again.
Russia doesn't have much oil storage capacity, so they'll be unlikely to store oil hoping to wait out the price cap. And Russia can't afford to stop the oil production.
While Russia may try to find other buyers, they are limited here as well. Most Russian oil is transported by sea, and the maritime insurance market is dominated by the G7. Chinese and Russian underwriters may step in, but they don't have nearly the capacity, particularly for reinsurance.