Depends on your users. A company I work with has clients who sign agreements annually, so their standard deprecation period is... one year. If people are buildi

Depends on your users. A company I work with has clients who sign agreements annually, so their standard deprecation period is... one year. If people are building commercial products or internal tools on your API, you've got to give them longer IMO. Also it makes sense to phase deprecation. Start by no longer issuing new API keys. If your API has a messages or comments field in the return object, you can add a notice that it's deprecated with a link to the new API to discourage new development. The biggest thing (IMO) is to make the transition process painless. If there's functionality that v1 has that v2 doesn't, users who like that functionality will cling to v1. If there's an endpoint in v1 with no clear equivalent in v2, that's gonna slow adoption unless there's a clear transition process documented somewhere.