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The latest version of the FHIR DSTU2 specification can be found searching the directory of releases at: http://www.hl7.org/fhir/indexdirectory.html. The changes most likely to impact an existing app would be any changes to a specific FHIR Resource that an app is using. Refer to http://www.hl7.org/fhir/resourcelist.html for the directory above, then find latest dstu2 and go to resources for FHIR Resource changes. If your app loads its own data into the sandbox using FHIR transactions, the transaction specification has several changes. Refer to http://www.hl7.org/fhir/DSTU2/http.html#transaction for transaction changes.
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The structure of the Conformance Statement's automated discovery of OAuth2 endpoints has changed. If you are using the latest (DSTU2) fhir-client.js, the client will handle this and you will not need to modify your app further. Refer to: http://fhir-docs.smarthealthit.org/argonaut-dev/authorization/conformance-statement/
New Launch Sequence
The launch sequence has changed. If you are using the latest (DSTU2) fhir-client.js, the client will handle this and you will not need to modify your app further. Refer to: http://docs.smarthealthit.org/authorization/
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