Simple script to insert data
Just 1 will work here.  It will do a cast to 1

SET @IsActive = 1  


You can also assign in the declare 

DECLARE 
      @Model_ID INT
    , @ModelVersion VARCHAR(10) = 'lasdf'
    , @ExistsInDM INT
    , @IsActive BIT = 1


SELECT  @Model_ID = Model_ID
FROM    [sch_AM].[tblDMModelVersion] WITH (NOLOCK)
WHERE   [ModelVersion] = @ModelVersion 


Above will get the last value read.  

with (nolock)


Is typically not advised.