Marketo has been communicating this architectural change to its customers worldwide since August of 2016, yet only lately it has become clearer that the change will affect more than a few fields. Specifically this is true for Marketo customers whose Salesforce CRM edition is the Professional edition.
Tip: if you're unsure which edition your Salesforce org is running on, log in to your account there and simply hover the cursor on the browser tab where Salesforce loaded. The tab tooltip will show you the edition.
If you're not a Salesforce Pro user, you can stop reading here; the change won't affect you beyond the 16 fields that you were asked by Marketo to recreate in Salesforce (see here
, Marketo login required).
However, if you are a Salesforce Pro and Marketo customer, now is the time to ensure your Salesforce subscription includes API calls. These can be purchased as a separate add-on. Your Salesforce org admin should know how to do that. However, if your org doesn't have API calls yet and you don't purchase them, after January 31st your Marketo-Salesforce sync will stop working
Here's what Marketo's @MarketoCares account wrote in reply to our clarification request today: "The fields won't be able to update data from Marketo to Salesforce without having the API calls there to pass the data. So, API access to SFDC will need to be enabled to use both these 16 affected fields and/or the rest of the Marketo > Salesforce sync." And this is what one of Marketo's reps wrote on a discussion thread in the user community: "Customers on Salesforce Professional Edition will need to purchase API access from Salesforce in order allow those API calls..."
So don't wait and take action.