This new library is meant to answer an inherent problem with the older open-source encryption programs: Their optional extensions make them very complex. Indeed, "OpenSSL, the de facto reference implementation, contains more than 500,000 lines of code with at least 70,000 of those involved in processing TLS. Naturally with each line of code there is a risk of error, but this large size also presents challenges for code audits, security reviews, performance, and efficiency."
Rather than try to cover all of SSL/TLS's full range of extensions, s2n, with its mere 6,000 lines of code, focuses only on encryption. This means that Amazon is not trying to replace OpenSSL. Schmidt wrote that "Amazon remains committed to supporting [OpenSSL] through our involvement in the Linux Foundation's Core Infrastructure Initiative."