Which master's specialisation in Germany suits a BTech Computer Science graduate with AI/ML specialisation and 21 months of work experience?

Because your BTech specialisation and your 21 months of work experience are both already in AI/ML, the main decision is not whether to specialise but how narrow to go, since a pure AI degree, a Data Science degree, and a Computer Science degree with AI electives each open slightly different doors in Germany.

MSc Artificial Intelligence or Machine Learning: The Direct Continuation

This is the closest match to your existing background. Strong German options include the University of Tubingen, known for its machine learning research ecosystem, the Technical University of Munich for its applied AI and industry links, and Saarland University for its informatics and AI research environment. Prioritise programs with deep learning, NLP or computer vision, and MLOps content depending on what your 21 months actually covered.

Data Science or a Broader Computer Science Track as Alternatives

• Data Science or Data Engineering: a strong alternative if your work experience leaned toward SQL, pipelines, and cloud platforms rather than model building.
• Computer Science with an AI specialisation: useful if you want more software engineering flexibility alongside AI, such as the AI track within the University of Freiburg's Computer Science master's.

My Advice

In my experience, candidates with genuine AI/ML work experience should avoid a very theoretical AI program unless they specifically want a PhD afterward, since a practically oriented AI or Machine Learning master's converts existing experience into a stronger German job application faster than starting over in a broader Computer Science degree. Be specific in your application about which part of AI your 21 months covered, whether NLP, computer vision, or generative AI, since it changes which university's research strengths line up best with your profile.