Which API architectural style should an integration architect choose to accept both XML and JSON content over HTTP/1.1?

The choice of REST as the API architectural style for accepting both XML and JSON content over HTTP/1.1 is appropriate due to its flexibility in content negotiation. REST APIs utilize standard HTTP methods and can accommodate various data formats like XML and JSON without requiring stricter contracts, as found in other styles such as SOAP. This adaptability allows clients to specify the desired format in their request headers, making it straightforward to handle different content types.

Additionally, REST's stateless nature and reliance on standard HTTP features make it particularly suited for web interactions. It also benefits from widespread adoption, meaning that many clients and libraries can easily consume REST APIs in either XML or JSON format.

While SOAP is designed to work primarily with XML and has more rigid protocols, it doesn't inherently support JSON format. GraphQL is focused on providing a more structured query capability and is also optimized for handling JSON, but it does not inherently support XML at all. gRPC, being a protocol based on HTTP/2 and often using Protocol Buffers as its serialization format, is not suited for XML content either. Thus, REST stands out as the most versatile option for providing support for both XML and JSON.