jdk.httpclient.keepalive.timeout, jdk.httpclient.keepalive.timeout.h2 and (in upcoming Java 26) jdk.httpclient.keepalive.timeout.h3 system networking properties are specified in the java.net.http module https://docs.oracle.com/en/java/javase/25/docs/api/java.net.http/module-summary.html#jdk.httpclient.keepalive.timeout

That specification currently doesn't explain how the HttpClient behaves when these values are configured with the value 0 or anything less than 0.