WP version compare with beta snapshots

Hey folks.

I’ve just installed 2.6-beta1. In order to test plugin compatibilities, I used the version_compare php function. I’d like to insert some code in 2.6-beta1 but not in 2.5.1. I’ve tried this:

if ( version_compare( $wp_version, '2.6', '>=' ) ) {
  // some code
}

but the code doesnt execute in 2.6-beta1. The version_compare did work a hundred times on other parts of the code.

Don’t I see the wood for the trees?

edit. Since actually 2.6-beta1 is earlier than 2.6, I’ve also tried

if ( version_compare( $wp_version, '2.5.9', '>=' ) ) {
  // some code
}

but that didnt work either.

Regards.