Altstaedt regularly performs on period instruments with ensembles such as Il Giardino Armonico with Giovanni Antonini, B’Rock with René Jacobs, Orchestre des Champs-Elysées with Phillippe Herreweghe, and Arcangelo with Jonathan Cohen. As a conductor, he has forged close partnerships with Orchestre Philharmonique de Radio France, Münchener Kammerorchester, Tapiola Sinfonietta, Scottish Chamber Orchestra and Les Violons du Roy.

Joint appearances with composers such as Thomas Adès, Jörg Widmann, Thomas Larcher, Fazıl Say and Sofia Gubaidulina consolidate his reputation as an outstanding interpreter of contemporary music. Wolfgang Rihm, Sebastian Fagerlund, Erkki-Sven Tüür, Marton Illés and Helena Winkelman have recently written concertos and other works for him. New concertos by Liza Lim and Malika Kishino as well as a new work for cello and choir by Raquel García-Tomás receive their premieres this season. 

In 2012 Altstaedt succeeded Gidon Kremer as Artistic Director of the Lockenhaus Chamber Music Festival, and from 2014 to 2021 he succeeded Ádám Fischer in this position at the Haydn Philharmonie at the Ésterházy Palace, touring with the orchestra to Japan and China in recent seasons. As a chamber musician, his partners include Janine Jansen, Vilde Frang, Pekka Kuusisto, Lawrence Power, Antoine Tamestit, Alexander Lonquich, Mao Fujita, Maxim Emelyanychev, Fazıl Say, Jean Rondeau, Thomas Dunford, Quatuor Ébène and Belcea Quartet. He performs at both Salzburg Mozart and Summer festivals, Verbier Festival, BBC Proms, Lucerne Festival, Edinburgh International Festival, Prague Spring Festival and Musikfest Bremen. 

His most recent recording for his Lockenhaus Festival garnered the BBC Music Magazine 2020 Chamber Award and Gramophone Classical Music Award 2020. He received the BBC Music Magazine Concerto Award 2017 for his recording of CPE Bach Concertos on Hyperion with Arcangelo and Jonathan Cohen and the AFAS Edison Klassiek 2017 for his recital recording with Fazıl Say on Warner Classics. Altstaedt is a recipient of the Credit Suisse Award in 2010, Beethovenring Bonn 2015, Musikpreis der Stadt Duisburg 2018 and was a 2010-12 BBC New Generation Artist.