Marketed as topical botulinum toxin, which is a comparison the underlying pharmacology does not really support.
what it is
Acetyl hexapeptide-8 is a fragment modelled on SNAP-25, a protein in the SNARE complex that neurons use to release neurotransmitter. Botulinum toxin cleaves that machinery; argireline is proposed to interfere with its assembly. The mechanistic analogy is real but the magnitude is a different matter entirely.
what the evidence shows
Small topical studies report modest reductions in expression-line depth over weeks of application. The measured effects are consistent enough to say something is happening and small enough that they are difficult to see without instrumentation.
Marketed as topical botulinum toxin, which is a comparison the underlying pharmacology does not really support.
what stays uncertain
Penetration is the central problem. A hexapeptide must cross the stratum corneum in sufficient quantity to reach neuromuscular junctions sitting well below the dermis, and the evidence that meaningful amounts arrive is weak. Most studies are small and funded by ingredient suppliers.
the practical note
Treat the injectable comparison as marketing. It is a well-tolerated cosmetic ingredient with a small measurable effect, which is a perfectly respectable thing to be without the borrowed prestige.