As described at https://help.salesforce.com/apex/HTViewSolution?urlname=How-do-unique-IDs-work-in-Salesforce-1327108651310&language=en_US, Salesforce has both 15-character and 18-character versions of its IDs, and the API defaults to using the 18-character versions. Unfortunately, the Salesforce UI defaults to using the 15-character version.
While it's possible to convert between them, as described at How can I convert a 15 char Id value into an 18 char Id value?, this isn't ideal, since it often requires us to ensure that software we write that deals with Salesforce IDs is aware of both forms and able to handle them. Code outside Salesforce that naively assumes that a Salesforce record has a single ID may be subtly broken, yet this is a seemingly reasonable and obvious assumption for a developer who doesn't know better. (This trap just bit me, which is how I learned about the two ID types.)
Is there a way to configure a Salesforce instance to use 18 character IDs everywhere, so I never have to think about the two kinds of ID again?