Boulez's 80th birthday was, of course, celebrated last year and the première of the Quatrième Sonate was evidently given on 19 February (in a fascinating concert series to mark that birthday which also included the world première of Carter's Réflexions, composed for the occasion. The 19 February concert was the last in the series and evidently consisted of Incises and Douze Notations, played by Hidéki Nagano, the Deuxième Sonate played by Dimitri Vassilakis and the Troisième Sonate and Quatrième Sonate played by Michael Wendeberg. Curiously, the Quatrième Sonate was not billed on that occasion as a première. I have not yet heard it or seen its score. All the performers on this occasion were, perhaps unsurprisingly, pianists closely associated with Ensemble Intercontemporain. Clearly, this programme was designed as a Boulez piano conspectus without the Première Sonate. Even though almost a year has elapsed since this occasion, I have to confess to being as sorry as I am ashamed to admit that this is still just about all that I know and can say about Boulez's Quatrième Sonate; this puzzles me not a little, for one would have imagined that there'd have been plenty of information around by now. Indeed, I cannot so far even run to earth any reviews or details about subsequent performances of the work.
Sorry not to be more helpful right now.
Best,
Alistair