“Over the past two years, however, the landscape has shifted; many more pre-trained models are now available. Given these changes, we see an advantage in making greater use of third-party LLMs alongside our own. This allows us to devote even more resources to post-training and creating new product experiences for our growing user base.”
My interpretation is that Character.AI realized they don't actually need to train their own foundation models from scratch to support their product - they can build cheaper, faster and probably better if they use LLMs trained by other companies (could be GPT-4o/Claude/Gemini via APIs, could be Llama 3.1 self-hosted).
If they're not training foundation models any more, the talents of people like Noam Shazeer aren't so important to them. They need to focus on product development instead.