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In general this release is backwards-incompatible only with regards to the Servlet API. In order to make it possible to run old code the Eclipse Transformer should be used during runtime through a weaving hook (in addition to the option to use it at compile time, e.g. with https://github.com/eclipse/transformer/blob/main/maven-plugins/transformer-maven-plugin/README.md). For everything else this major release is fully binary backwards-compatible!
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