problem with "composer require drupal/php 8.1.0-beta2"

the Composer command composer require drupal/php 8.1.0-beta2 ends up with a failure installation message.

I successfully installed PHP extension on Drupal 8.1.0 via the following order : composer require drupal/php ~8.1.* (or something like this, I am not sure any more).

BUT the PHP extension which has been installed is php 8.1.0-beta1
WHILE le last version of this PHP extension is php 8.1.0-beta2
SO I try to force the version I ask through my composer command...

the result is KO, see below

pi@raspberrypi:/var/www/html $ composer require drupal/php 8.1.0-beta2
./composer.json has been updated
No patches supplied.
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Installation request for drupal/php 8.1.0-beta2 -> satisfiable by drupal/php[8.1.0-beta2].
    - drupal/php 8.1.0-beta2 requires drupal/filter dev -> no matching package found.

Potential causes:
 - A typo in the package name
 - The package is not available in a stable-enough version according to your minimum-stability setting
   see <https://getcomposer.org/doc/04-schema.md#minimum-stability> for more details.

Read <https://getcomposer.org/doc/articles/troubleshooting.md> for further common problems.

Installation failed, reverting ./composer.json to its original content.

pi@raspberrypi:/var/www/html $