Bullet 2.49 is released (minor bug-fixes for Bullet 2.48a)
A refit function for the bounding volume hierarchy (btOptimizedBvh, quantized stackless aabb tree) has been added. This allows to refit the tree when the triangle meshes are deforming.
See the ConcaveDemo for an example how to use this new feature. Objects might deactivate early when animating slowly, so be careful with activation strategies.
Note that some features like setAngularFactor, and custom friction model callbacks don't work yet with the 'cache friendly' solver mode.
If you rely on those features, you can switch to original (non-cache-friendly) solver mode:
btSequentialImpulseConstraintSolver* solver = new btSequentialImpulseConstraintSolver;
//default solverMode is SOLVER_CACHE_FRIENDLY and SOLVER_RANDMIZE_ORDER.
//Switch back to original solver (non-cache friendly):
Bullet 2.49 source code.