Shopify Subscriptions API is currently in beta and will be available as a stable API release early next year.
The new offering only impacts the subscription checkout process–and does not impact post-purchase (e.g. customer portal).
Stripe, Braintree and other payment providers are not enabled yet. Merchants have to use Shopify Pay.
Merchants can enable free shipping for subscribers but cannot offer a percent discount on shipping.
The new offering does not enable trial subscriptions.