[RadioactiveMan]

Here's the RFC for it with the "why" and discussion of the tradeoffs. https://wiki.php.net/rfc/numeric_literal_separator

[tyingq]

Underscores in numeric literals are also now pretty much a defacto standard. Java, JavaScript, Perl, Python, C#, Ruby, Rust, Swift, etc, all support it.

[GrumpyNl]

Thanks for the link.