  We derive the protected closed-string spectra of AdS3/CFT2 dual pairs with 16
supercharges at arbitrary values of the string tension and of the three-form
fluxes. These follow immediately from the all-loop Bethe equations for the
spectra of the integrable worldsheet theories. Further, representing the
underlying integrable systems as spin chains, we find that their dynamics
involves length-changing interactions and that protected states correspond to
gapless excitations above the Berenstein-Maldacena-Nastase vacuum. In the case
of AdS3 x S3 x T4 the degeneracies of such operators precisely match those of
the dual CFT2 and the supergravity spectrum. On the other hand, we find that
for AdS3 x S3 x S3 x S1 there are fewer protected states than previous
supergravity calculations had suggested. In particular, protected states have
the same su(2) charge with respect to the two three-spheres.
