Funny thing, TypingMind was ahead of them for over a year, implementing those features on top of the API, without trying to mix business model with engineering[0]. It's only recently that ChatGPT webapp got more polished and streamlined, but TypingMind's been giving you all those features for every LLM that can handle it. So, if you're looking for ChatGPT-level frontend to Anthropic models, this is it.
ChatGPT shines on mobile[1] and I still keep my subscription for that reason. On desktop, I stick to TypingMind and being able to run the same plugins on GPT-4o and Claude 3.5 Sonnet, and if I need a new tool, I can make myself one in five minutes with passing knowledge of JavaScript[2]; no need to subscribe to some Gee Pee Tee.
Now, I know I sound like a shill, I'm not. I'm just a satisfied user with no affiliation to the app or the guy that made it. It's just that TypingMind did the bloodingly stupid obvious thing to do with the API and tool support (even before the latter was released), and continues to do the obvious things with it, and I'm completely confused as to why others don't, or why people find "GPTs" novel. They're not. They're a simple idea, wrapped in tons of marketing bullshit that makes it less useful and delayed its release by half a year.
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[0] - "GPTs", seriously. That's not a feature, that's just system prompt and model config, put in an opaque box and distributed on a marketplace for no good reason.
[1] - Voice story has been better for a while, but that's a matter of integration - OpenAI putting together their own LLM and (unreleased) voice model in a mobile app, in a manner hardly possible with the API their offered, vs. TypingMind being a webapp that uses third party TTS and STT models via "bring your own API key" approach.
[2] - I made https://docs.typingmind.com/plugins/plugins-examples#db32cc6... long before you could do that stuff with ChatGPT app. It's literally as easy as it can possibly be: https://git.sr.ht/~temporal/typingmind-plugins/tree. In particular, this one is more representative - https://git.sr.ht/~temporal/typingmind-plugins/tree/master/i... - PlantUML one is also less than 10 lines of code, but on top of 1.5k lines of DEFLATE implementation in JS I plain copy-pasted from the interwebz because I cannot into JS modules.