sp_prepexec (sp_execute) vs. sp_executeSQL The meat of the question: are actual stored procedures the only mechanism that implements temp table caching or do system stored procedures such as sp_executeSQL / sp_execute also take advantage of them?

I am not a DBA, so please use little words. Our application sends over prepared statements that, from the profiler, I see run all SQL through sp_prepexec which is a system procedure for both running sp_prepare and sp_execute. What I'm trying to do is figure out if I am benefiting from temp table caching. 

I've been using this guide with object_id() to examine behavior

https://sqlkiwi.blogspot.com/2012/08/temporary-tables-in-stored-procedures.html

Then point #3 on this blog post suggests that EXEC cannot use temp table caching, but leaves out whether sp_executeSQL can:
http://blogs.msdn.com/b/turgays/archive/2013/09/18/exec-vs-sp-executesql.aspx

In my query sent over via the client I have created a simple temp table.

DECLARE @foo int; -- set by JDBC, unused but required to force a prepared statement

SELECT 1 AS id
    INTO #tmp

SELECT OBJECT_ID('tempdb..#tmp');


In profiler, I can see:

declare @p1 int
set @p1=NULL
exec sp_prepexec @p1 output,N'@P1 int',N'declare @foo INT = @P1 

SELECT 1 as id
    into #tmp

select Object_id(''tempdb..#tmp'');
DROP TABLE #tmp;',1
select @p1


I also get a cachehit from this. However, the object_id of the temp table appears to be changing on me, which is not the behavior I would see if this temp table were created in a real stored procedure. However, when I run this same code through sp_executeSQL, I'm also seeing that the object_id of the temp table has changed. This leads me to believe that only "real" user created stored procedures take advantage of temp table caching.
Are actual stored procedures the only mechanism that implements temp table caching or do system stored procedures such as sp_executeSQL / sp_execute also take advantage of them?


You need a real stored procedure (CREATE PROCEDURE) to benefit from temporary table caching. This includes temporary stored procedures (#procname).


  Point #3 on this blog post suggests that EXEC cannot use temp table caching, but leaves out whether sp_executeSQL can.


Notice that EXECUTE is used to run sp_executesql.

Testing: There are many ways to check whether caching is occurring. Some of them are listed in my original article referenced in the question, some more methods are shown in my follow-up post, Temporary Table Caching Explained, for example:

SELECT 
    DOMCC.name,
    DOMCC.pages_kb,
    DOMCC.pages_in_use_kb,
    DOMCC.entries_count,
    DOMCC.entries_in_use_count
FROM sys.dm_os_memory_cache_counters AS DOMCC
WHERE DOMCC.[type] = N'CACHESTORE_TEMPTABLES';


Stored procedure input TVPs are also cached, and starting with SQL Server 2012, these can also be cached when used with sp_executesql. See the linked CSS blog post for details.