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For anybody coming to this more recently, The REST API (v1.0) has now been retired with v1.1 being the only version. This Does now require authentication for everything, including reads.
Authentication required on all endpoints
In version 1.1, we're requiring applications to authenticate all of their requests with OAuth 1.0a or Application-only authentication. Not only will this visibility allow us to prevent abusive behavior, but it will also help us to further understand how categories of applications are using the API. We'll apply that understanding to better meet the needs of developers as we continue to evolve the platform. At this time, all authentication requires user context, but in the coming weeks we'll be pushing out support for a form of authentication not requiring a user context.