Today is traditionally called Spy Wednesday, the Wednesday in Holy Week, remembering that Judas Iscariot went today to the priests of the Temple to betray the Lord. The Passion according to Saint Luke is read at Holy Mass. The Office of Tenebrae follows, in the evening after Vespers, being the Hours of Matins and Lauds of Holy Thursday; this is being streamed from Saint-Eugène at 1100 or 1130, one or the other.
If I were actually able to attend at it, I'd say the Office through Vespers beforehand but since I'm following online, which has only a very qualified character of 'attendance at', will say my own Office as usual with the exception that Sext is on the agenda within the hour. More or less.
The livret* for Tenebrae at Saint-E. is here. According to the post at Liturgia, François Couperin's setting of the three Lessons will be sung, Giovanni Battista Martini's setting of the Responsoria, and the Miserere of Guillaume-Gabriel Nivers.
Since there are nine Lessons, and Couperin composed settings for the three of the 1st Nocturn only, am going to presume that the other six will be chanted as usual. ['Chanted as usual', yes, but there is a proper tone for them which features a lovely cadence.]
Post Officium Tenebrarum. A lovely and moving celebration of the Office. Had it been up to me, I would have omitted the Nivers Miserere (and sung it another day, I mean) so that the Christus factus est would be the final chant. (What was sung at Saint-Eugène was the traditional antiphon, ending obediens ad mortem. Tomorrow, the mortem autem crucis will be added, and at Lauds of Holy Saturday, the completion of it, propter quod et Deus exaltávit illum, et dedit illi nomen quod est super omne nomen. But I cannot easily find a recording of today's part only, eh, so this one will do.)
Christus factus est pro nobis obédiens usque ad mortem.
*There is a misprinting in the libellum: Vigils are Matins, Matins are Vigils, and what is meant by 'à Matines' on page 34 is Lauds. I recall being rather discomfited by this last year, ha, if only briefly.