I know that Car IT has a large group there which originates from the Nokia office in Ulm. They also have lots of hiring postings on stackoverflow careers. But I don't really know how much they are doing in house within that group and which parts will still be externally sourced. Even if they are now doing more parts of the headunit themselves there will be still lots of other ECUs which are 100% external developments. For infotainment BMW probably has the most in-house efforts going on. Audi went another route and founded e-solutions as a joint venture together with Elektrobit, which is developing exclusively for Audi. Daimler is still mostly relying on external partners.