For all the people asking "Why?", it seems like TFA has a pretty good list of features/attributes that it thinks sets it apart:

- fx is a coding agent harness and CLI written in Zig, optimized for research and embeddability as part of larger systems.

- It focuses on minimalism and performance across the board, from system prompt design, to its tools, feature set, and 6.39mib binary.

- For end users, its CLI output style and form factor aims to be closer to a Unix shell than a heavy "IDE in the terminal" TUI.

- It's open source (Apache-2.0), model-agnostic, and suitable for both local and cloud inference.

- Designed for instant installation and embedding in resource constrained environments and agent sandboxes.

- fx cold starts in 10µs and does no unnecessary work or I/O prior to accepting user input, making it ideal for programmatic use.

- Optimal fx.wasm builds produced by the Zig toolchain, which further reduce fx's size, making the network stack pluggable.

- fx contributes single-digit megabytes of memory baseline, allowing you to pack many instances in one machine.

- fx preserves scroll history by default, produces minimal output, and makes sparing use of complex TUI or paints

- Minimal system prompt and tools, to save on token costs and to yield optimal time-to-first-token performance (TTFT).

- Small core, extended via skills, plugins, MCPs, with a Unix-like philosophy to extensibility.

- Designed to work with local models, gateways, direct provider API access or subscriptions.

If you like this list of "why?", you might also like this: https://usehax.dev/ (I am the author). Most of the list applies, similar minimalist Unix tool approach, with some differences. Hax is written in C, the dynamically linked binary is even smaller (0.6 MB), MIT-licensed. No wasm though.

Important difference - fx is currently Vercel AI Gateway only - while hax does support multiple providers already (OpenAI API, ChatGPT/Codex subscription, Anthropic API, OpenRouter, OpenCode Zen/Go), and integrates well out of the box with local llama-server.

Very neat. The demo on the page feels very intuitive to me! (if you're used to bash at least)

I've only done a little of the new opencode v2 "mini" but it too offers a nice preserve-scroll by default.

OpenCode is the best behaved TUI i've seen by far (they invented OpenTUI to make it so good, also in Zig), so it feels less crucial. But it's nice to have there!

The "small core" model is very popular all of a sudden. DeepSeek's new harness is famously like that. https://news.ycombinator.com/item?id=49285244

OpenCode isn't quite as small, but there's very much been a deliberate attempt to drive much more into a plugin-based system. I enjoyed Dax talking about the new constitution of opencode, and the results of his agent comparing OpenCode & the new DeepSeek. https://bsky.app/profile/thdxr.com/post/3msy4gjttoc2f https://bsky.app/profile/thdxr.com/post/3msygiqyg6v2y

> an architectural change we made in opencode2 is nearly everything is an internal plugin / there's 68 of them that cover our built in agents, integrations, config loading, etc

i also think this is such a brilliant fun architectural twist too:

> OpenCode is the first time i could justify event sourcing in a real system / everything that happens is an event which gets projected into the sqlite db

https://bsky.app/profile/thdxr.com/post/3mt2qx3ktib2c

it's so fun seeing new malleable software cores emerge, try to figure out how to augment agency. agentic software striving itself to extend the agency it itself offers. it's been way too long since we've had ambitions to build general system, architectures that serve more than the user. this has held computing back for far too long. this is such an excellent interesting field, of such a more ambitious computing, opening up.

Most of all what you have said is not really any clear differentiation against the rest of the 100s of other agents. Just minuscule or non-negligible implementation details and I'm afraid it is sadly yet another experimental slop project.

It is a branded "mee too" coding agent that we have seen hundreds of them already.

"- For end users, its CLI output style and form factor aims to be closer to a Unix shell than a heavy "IDE in the terminal" TUI."

I've actually been wondering lately why coding agent functionality isn't just... part of my shell already. Just another kind of interaction modality with an existing shell. Could probably even be an extension to fish or nu-shell even.

Please stop me from forking off on yet another project though.