What is the Pronunciation of "-sts" at the end of the word?

How can we pronounce words ending with -sts?

• lists
• costs
• tests

I often heard people pronunce its like,

• lɪsts and kɒsts
• lɪsː kɔsː
  

but which one is acceptable?

In rapid speech particularly, consonants in clusters such as /sts/ are frequently lost in a process known to phoneticians as ‘elision’. Similarly, ‘next’ will occur as /neks/ and ‘acts’ as /aks/. It’s not so much a matter of bad pronunciation as a recognized feature of speech which most of us will display at one time or another.

Imagine the conversation, over a bad phone line.

Alice: Let's talk about the kɒsː associated with with this project

Bob: I'm sorry, "Coss"?

Alice: No. kɒsts. C.O.S.T.S.

Bob: Ah, sorry, you were speaking too quickly.

These are simple words that are said as they are written -- nothing to catch us out as with trough and plough.

But in English, as I believe with almost every language, people tend to rush over words. This is how going to becomes gonna.

So, it's kɒsts and lɪsts, when spoken by the Queen or a newsreader, but the t might disappear in everyday conversation.

The accepted pronunciation of '-sps', '-sts', and '-sks' is to drop the stop, and the 's' may or may not be extended (as though it were a doubled s). It is not frowned upon at all to not pronounce the p, t, k, even in slower speech.

In expected-articulate speech, say newscasters and actors, there will be a tendency to not drop.