Actually, it is possible so serve compressed HTTP content using current SA versions, but it requires some additional coding (see example below). So, a built-in HTTP compression would still be a more robust and usable solution. P.S. You can check if your page is compressed using this online tool: Port80 Software

CREATE FUNCTION "sp_client_accepts_encoding"(IN @Algorithm CHAR(100))
RETURNS INTEGER
BEGIN /* returns 1 if client (browser) accepts given HTTP compression algorithm (according to Accept-Encoding HTTP header values) */
    DECLARE @List LONG VARCHAR;

SELECT value INTO @List FROM sa_http_header_info('Accept-Encoding');
    IF EXISTS (select 1 from sa_split_list(@List) where row_value = @Algorithm) THEN
        RETURN 1;
    ELSE
        RETURN 0;
    END IF;

END

GO

CREATE FUNCTION "sp_compress_page_if_accepted"(IN @HTML_page LONG BINARY)
RETURNS LONG BINARY
NOT DETERMINISTIC
BEGIN
    IF sp_client_accepts_encoding('gzip') = 1 THEN // client (browser) accepts compression
        CALL dbo.sa_set_http_header('Content-Encoding', 'gzip');
        RETURN COMPRESS(@HTML_page, 'gzip'); // return compressed page
    ELSE
        RETURN @HTML_page; // return uncompressed page
    END IF;
END

GO

CREATE SERVICE "hello" TYPE 'RAW' AUTHORIZATION OFF USER "dba" AS 
SELECT sp_compress_page_if_accepted('Hello, world!');

Another solution for current versions of SQL Anywhere is to sit the database server behind a Reverse Proxy that is capable of compressing the responses. E.g. Apache via mod_proxy or the latest versions of IIS (7.0 and 7.5).