Are there any useful alternative models though? Most I've found weren't particularly good at following instructions or using tools in the way langchain provides them.

FYI, the upcoming version of gpt4 does considerably worse emulating function calls / generating code-like strings, but gets better again if you switch to the function call API: https://twitter.com/reissbaker/status/1671361372092010497

(My guess is the same is true of gpt-3.5, although I haven't tested it.)

That being said, Langchain has a nearly drop-in replacement if you want to start using the function call API: https://python.langchain.com/docs/modules/agents/agent_types...