In a medium bowl, whisk together chia seeds, almond milk, maple syrup, almond butter, and vanilla extract until well combined and no clumps remain.
Let the mixture sit for 10 minutes, then whisk again to prevent the chia seeds from sticking together.
Gently fold in 3/4 cup of the raspberries, lightly crushing a few with the back of a spoon to release their juices.
Cover the bowl and refrigerate for at least 4 hours or overnight, until the pudding is thick and creamy.
Before serving, give the pudding a good stir. If it's too thick, stir in a splash of almond milk.
Spoon into serving glasses or bowls. Top with the remaining 1/4 cup raspberries and toasted sliced almonds, if desired.