The lambda implementation requires the MethodHandle/invokeDynamic work introduced at 7, and run time components introduced at 8. There is also some significant

The lambda implementation requires the MethodHandle/invokeDynamic work introduced at 7, and run time components introduced at 8. There is also some significant work being done on the inliner to support better optimisation for lambdas. Further to that 8 introduces default implementations to interfaces to allow lambda exploiting features to be added to the standard Java APIs while allowing old code to be run without requiring recompilation. Though changes to the instruction set do not happen at every release there are normally changes to the class file format - so although generics were implemented by type erasure at Java 5 so did not need an instruction set change new signature information was added to the class file format to describe the type parameters, and annotations were introduced which required further class file format changes.