Test version is live: much obliged! (4)
I believe the answer is:
beta
'test version' is the definition.
(I've seen this in another clue)
'live much obliged' is the wordplay.
'live' becomes 'be' (synonyms).
'much obliged' becomes 'ta' (both are ways of saying thank you).
'be'+'ta'='BETA'
'is' is the link.
(Other definitions for beta that I've seen before include "Greek character - not quite top-notch" , "testing stage" , "In a constellation, a star second in brightness" , "Second Greek letter, B" , "Greek letter -- second in order of importance" .)