I just got an email from Anthropic telling me they are deprecating their good model, which actually works well, claude-sonnet-4-5-20250929, and will be forcing all users to use the worse newer model, claude-sonnet-4-6. Okay, fine, I thought. Then I went to their model page to check what is the latest version of that model. They don't list any! The only version they list is "claude-sonnet-4-6", which, according to their own documentation, always refers to the newest version of Claude Sonnet 4.6. This means that the client applications I've built using Sonnet will unpredictably break at random times when the model version changes. I tried contacting Anthropic customer support, but of course they don't have any actual humans, they only have an AI chatbot (chatbot called "Fin", OUTSOURCED from Intercom, which is notoriously bad at making chatbots). Their AI chatbot tells me that if I use the version "claude-sonnet-4-6", it will always refer to the latest model version, so I should instead pin to the specific version, "claude-sonnet-4-6". Those strings are the same. Anthropic's AI chatbot does not seem to comprehend that they are the same strings. I also checked the model listing in their API playground and I checked the docs, and there's absolutely no way to pin a specific version anymore.