Nope they have supported AWS deployments for a long time, and now even more of the spend will be on AWS.
> Anthropic has raised an additional $4 billion from Amazon, and has agreed to train its flagship generative AI models primarily on Amazon Web Services (AWS), Amazon’s cloud computing division.
Yes, they are currently on GCP. What you wrote said they will train their flagship generative AI model primarily on AWS.
Wouldn't be hard to code it to easily swap between GCP and AWS ahead of time knowing things like this could happen