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The runtime will be built in terms of the NS* level of classes, and is probably not very optimized in the first versions. I'll identify hotspots later and maybe add a CF-based runtime for speed if it turns out to be a problem.
The layout of the runtime is essentially the same as the Java version, though subtle differences will be visible where it makes it more natural to the Objective-C programmer. Naming of classes and methods may be slightly different and sometimes inner workings are too.
Initial tests don't show serious performance problems, though I'm sure there will be opportunities for optimization.
The biggest problem at the moment are the numerous unused variables created at the moment. Often ANTLR will build up lists of tokens but subsequently not use them in any significant way, which leads to wasting time and space. This can only be fixed in the ANTLR code generator and not for individual targets. I am looking into this.
Examples
The goal is to provide the complete set of Java-based examples in Objective-C for comparison. There may be additional examples contained in the Xcode project. These exist mainly for development purposes as testcases, or to try out features.
I am currently working on an editor for StringTemplates as a big "example"/testcase for v3.
Also take a look at the Xcode plugin that uses a filtering lexer written using ANTLR to figure out grammar types and dependencies.