In this release cycle we had to introduce a bunch parser hacks to avoid breaking existing code:

• In order to introduce new Yul opcodes in a non-breaking way, we had to mark them as exceptions for older EVM versions in createReservedIdentifiers():
  • basefee
  • prevrandao
  • tstore
  • tload
  • blobbasefee
  • blobhash
  • mcopy
  • clz
• Existing builtins have not been made reserved yet
  • memoryguard
• New keywords needed for storage layout syntax (Allow specifying storage locations #597):
  • at
  • layout
• New keywords needed for transient storage (High-Level Language Support for Transient Storage #15007)
  • transient
• Other identifiers that should become keywords:
  • error
  • super
  • this
  • leave (in Yul)

In the next breaking release the exceptions should be removed and keywords added.