There are a lot of things going wrong when trying to use IL2CPP for Windows standalone as build option with ML-Agents. I recently tried to build Puppo The Corgi demo and got first stuck with protobuffer not finding two internal methods: dlsym and dlopen. Turned out that these were only used on Linux but since they were in Grpc.Core.dll, IL2CPP code tried to link against them, ultimately failing to do so. I manually removed the offending parts as I'm not building for Linux but proper way to handle this would be to ship either ml-agents with platform specific dll for these or have sources there and have platform switches for these. After figuring out the protobuffer thing, IL2CPP build actually finishes but once run, it wouldn't work properly. Instead, logs would be full of things like these: So, ultimately the question is, will Unity make ML-Agents IL2CPP compatible in the future? Any thoughts from @JoshPeterson?