In Studio Pro, licensing Splice samples does not cost credits depending on your plan:
Splice x Studio Pro
Users with the Splice x Studio Pro plan can license up to 100 samples per day exclusively in Studio Pro without using credits.
Sounds+
Sounds+ users can license sounds in Studio Pro using credits only.
If you're on a Sounds+ plan and wish to license sounds in the DAW without credits, please either switch to the Splice x Studio Pro plan or upgrade to Creator or Creator+: splice.com/plans
Creator & Creator+
Similar to Splice x Studio Pro, Creator and Creator+ users can license up to 100 samples per day in Studio Pro without using credits.
All downloads outside of Studio Pro, such as the Splice Desktop App, website, or mobile app, will require credits.