With js you get 1 thread at 100% utilization. Power usage and heat scale non-linearly with cpu utilization and 100% utilization on a single threaded js app means you will have ui lag. Other languages like golang would split work across 8 threads and have 8 threads at 20% utilization and this would result in less power usage. Claude Code would have been better off performance wise being an electron app because it would be offloading rendering to the browser and gpu.
Also, the architecture of Open Code is actually a lot better here than Claude Code. ClaudeCode does everything, including rendering in a single thread and it's all in js. OpenCode has a zig based tui renderer it offloads that work onto.
But I will also say these coding agent tuis do get unfairly maligned because they launch subprocesses and those subprocesses tend to be expensive. If you are using Rust analyzer with claude code, it's rust analyzer that's causing the majority of your problems.
> they need a high powered game engine rendering loop
Don't believe the bs on twitter. Claude code source was leaked, there is no high powered game engine rendering loop.
> It needs to stream text to stdout
These apps are doing real work taking text that is streaming in and doing syntax highlighting, calculating diffs, and rendering markdown. If the work was split across threads they would not use anywhere close to as much power and there would not be a slow ui.
If you think this is actually nothing, prove it. Put the code up on github that shows taking a constant random stream of markdown, code, and diffs and displays it in the terminal can be done cheaply on a single thread.
The reason the computer gets hot and uses more power is because the cpu is getting close to 100% utilization.
> These apps are doing real work taking text that is streaming in and doing syntax highlighting, calculating diffs, and rendering markdown.
The first argument is that these are expensive operations. They are not. And the second argument is the assumption that these are desirable things for an agent system to be doing. That's a personal preference but, personally, I don't want them and would appreciate a way to disable all of that to reduce CPU use.
A lot of people go “js is bad” reflexively and they are right for the wrong reasons. Its not because js (specifically v8) is slow. I have many websites and web based apps open and none fuck up my laptop as hard as claude code.
The UI itself requires laughably simple tech. The idea that a markdown renderer that can produce HTML at 50MB/s would use much CPU to process incoming hundreds of bytes per second is insane. CPU should be idle even if doing that constantly. Nevermind that between turns it has nothing to do whatsoever and should use zero CPU at all.
I picked the P90 because I remember running Linux ~1.0 and/or NT on it, with real multitasking and services etc. Those soaked up many of the cycles.
Another story, around Y2k/Win2k was asked to write a C program to record all the files/sizes on the C: in to file. Then something would be installed, my program run again, and the results diffed. Despite thousands of files the program was done before the enter key came back up. Boss told me that he thought the program was cheating.
That’s just how fast modern computers are these days, I said. When running C code anyway. That perf is still available today, compare astral’s uv to slow competitors. Just takes some investment, though probably less when boosted by VC bionics.
— Henry Petroski
Casey Muratori addressed this years ago with the windows terminal drama, https://github.com/cmuratori/refterm
Put up the code and prove it. We already know exactly how fast golang is in comparison to nodejs on basic numeric computations, it's roughly 40 to 50% faster.
I don't doubt this, but I would love details and citations here.
Bad coding is just bad coding.
It's also all cpu bound work. The majority of the stuff on your screen is being rendered by the gpu.
You are really, really not. Not at LLM inference speeds at least. Frontier models output maybe 200 bytes per second on the fast end. I guarantee you that idle BSD box is still processing more than 200 bytes of whatever at any point in time. Streaming 200 bytes of LLM output through syntax highlighting, markdown rendering, and diff formatting, will still leave the box basically idle if done correctly. Claude Code has not done it correctly.
This does not even speak to it pegging my CPU and keeping the fans running on full blast even when the laptop is supposed to be idle overnight.
You could test this by running "yes > /dev/null" in Ghostty. In Activity Monitor on my Macbook it shows `yes` using 100% and Ghostty using 0.5% of cpu.
Never had to dig through the xterm bug tracker to figure something out. I don't even know what version I'm running, or even what the versioning scheme looks like. I haven't changed the configuration since the first time I set it up. It just works.
Then something is waking it up and it's not asleep at all. Asleep the CPU shouldn't be running.