WebSphere Liberty has supported it for a few years. HTTP/2 support is not planned for IHS. If IHS is the first HTTP proxy your clients hit and you want them to get the benefit of HTTP/2, you should use a different/additional proxy to terminate HTTP/2 closest to your client.
HTTP/2 for the traditional websphere application server, as opposed to Liberty, doesn't even seem to be formally tracked in a request for enhancement. Personally it sounds quite disruptive for little practical value for a stable server that is usually fronted by N layers of proxies.
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