Previously, German citizens lost their German citizenship if they took on another citizenship (such as U.S. citizenship). Since 2000, however, it has been possible to apply in advance for a retention permit from the Federal Office of Administration. To do so, you had to prove strong ties to Germany and explain the need for dual citizenship.
This is now changing with the new Act on the Modernization of Citizenship Law (StARModG), which was passed by the Bundestag on January 19, 2024 and comes into force on June 26, 2024. This means that after June 26 no longer requires a retention permit.
This makes life easier for German "expats" in the USA, who can now apply for U.S. citizenship without the formality of retention approval. In the past, the retention permit process took about a year, and then there was the U.S. naturalization process of about a year.
The new law also stipulates that multiple nationalities will generally be accepted in future.
Further information can be found on the Bundestag website: https://www.bundestag.de/dokumente/textarchiv/2024/kw03-de-staatsangehoerigkeitsrecht-986286
From the perspective of the recruiters at TH Bender & Partners, the leading German-American recruitment consultancy, these new regulations are of great importance for many Germans working in the USA. Not only does this new law shorten the time it takes for German citizens to obtain U.S. citizenship in the U.S., it also facilitates professional activities which de facto require U.S. citizenship. This is generally the case for jobs in government and public administration, see Executive Order 11935. This is also de facto the case for intelligence activities and specially controlled activities such as those covered by "International Traffic in Arms" (ITAR).
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