OpenRouter works great! I wrote a coding agent CLI that uses it, new models get added all the time. You can check out the code here: https://github.com/nerds-with-keyboards/flite/blob/main/bin/...

Your best bet is having an account on AWS Bedrock & Vertex AI so you're able to route your request to the same model (such as claude-sonnet-4) but on a different provider.