The standard payment frequency for all recurring payments processed by the Donations app is monthly. With a recent release of Soapbox, if you are using Authorize.net, CyberSource, or PayPal Website Payments Pro as your payment processor, you can override this standard behavior on a form by form basis to accept annual recurring payments instead. If if this enabled, any recurring payment created through that form - whether processed seamlessly on Soapbox via your payment processor or off-site via PayPal Standard - will be setup as an annual recurring transaction.
It is important to note that, as of now, support has not yet been added for onboarding initial Soapbox Recurring Donation records in Salesforce as annual transactions. This will be added by February 2018. If you wish to use this feature in the meantime with Salesforce, we suggest you create a unique Transaction Description for a Donation form set to process recurring payments annually and build automations in Salesforce to manage the data as you wish.