Hey, habe mich ein wenig informiert, das gleiche Problem hatten viele vor knapp 1-2 Jahren. Hier eine Antwort vom Steam Support:

"Hello and thank you for writing in.

I've taken a look and see that the free Counter-Strike: Global Offensive license does not currently include the SDK. However, with the transition to free to play I'm uncertain if it staying this way was intentional or not.

I'm forwarding this information onto the developers so they can look into it. While I do not know when or if an update may be rolled out, please know that the development team will review this.

However, at this time I do not have anymore information regarding the change.

If there is something else we can assist you with at this time, please let us know.

Steam Support

Jason"

Dazu habe ich herausgefunden, dass man den Hammer Editor NICHT nutzen kann, wenn man sich Prime erspielt hat. Man bekommt es nur, wenn man sich Prime für den Vollpreis erkauft!