Unreal Agent's async harness cuts coding agent costs by 40%
Unreal Labs built Unreal Agent with a fully asynchronous tool-calling harness that removes waits, polls, and heartbeats from the model's workload. The result: up to 40% lower cost than Codex and 20% lower than Pi on real workloads and agentic benchmarks like Terminal-Bench 4.0, SWE-Atlas, and DeepSWE 1.1, with comparable pass rates. The SDK ships as a Go library, a runner executable, and a Harbor-compatible benchmark runner.
The Unreal Agent harness manages tool calls in a completely asynchronous way, relieving the underlying model of the need to manage waits, polls, and heartbeats for tools.
- dvt
I think this space is very untapped. Models are interesting, but I am absolutely obsessed with some things I've been researching/working on for the past few years:
Fractal tool discovery: tool taxonomy where an agent can "drill deeper" to find what specific tool it's looking for. Helps if/when polluting context with a zillion (mostly unnecessary) tools.
Leveraging splay trees: this is my favorite data structure and I think relatively unused in the context of agents/harnesses. A lot of times, recently-used workflows/tool-chains will be used again, so having those at the top of the search hierarchy is an awesome optimization.
Virtual containerized notebooks: models working in sandboxed (WASI) Python notebooks is incredible. Even local models (if given enough time) will usually converge on a good solution. Being able to mount tools/resources/fs is again, imo quite untapped. Some problems here are running native things (thing numpy/pandas) in containers is a nightmare (or impossible).
Anyway, happy to see other folks seriously doing stuff in this space. If anyone wants to collaborate on anything don't hesitate to reach out :) I'm also actively looking for a job or some contract gigs.
Fun times ahead.
- ricardobeat
Crush [1] has had async tools for a long time, as has Claude Code.
They work well, except that the agent will often simply call wait() immediately after, and also do it with a longer timeout, causing crashes/hangs to really slow down the process; whereas immediate tool calls have a built-in 30s timeout in most harnesses.
I imagine this one will suffer from similar problems.
- tekacs
The headline graph is kind of bizarre.
For some reason they're comparing their harness running on Astra xhigh to Codex with Astra max?
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Also worth noting that OpenAI just added support for async tool calling to their harness, which isn't 1:1 with this approach, but is slowly ramping up in being able to provide something similar.
A big part of why Codex uses so many tokens is that it basically hot loops on polling tasks it starts for... absolutely no good reason: https://www.reddit.com/r/codex/comments/1wdlp7q/weve_discove...
I fixed it on my fork of Codex too, also back in Jan/Feb – I keep this patch rebased, for anyone who wants it: https://github.com/tekacs/codex/commit/9ffcf8db9078eae43d411...
It results in token savings similar in scale to those displayed here by Unreal.
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My harness has used a slightly fancier version of the approach that Unreal is using since ~Feb, and... it definitely works excellently, but it's also assuredly smoother with Astra and other recent models that are more aware of async tool calling.
- tapoxi
Sounds like a trademark issue when Epic ships a wildly popular Unreal Engine
- pyrolistical
Funny, I solved this problem by having Claude write a pi extension
https://github.com/Pyrolistical/pi-notify
Now my pi agent setups its own trigger to notify itself when a background process is done
- westoque
not a fan of README's where there's no clear way to run the program, like a getting started or how to build. i think this is the opposite of a docu-monster where AI documents everything, but clearly more documentation is better than lack of.
- ozozozd
I suppose GPT models throw shade when your input is less favorable to Codex:
“On the surface, Unreal Agent achieves the same outcomes with fewer model turns and fewer input tokens.”
(Emphasis mine)
- tontinton
Oh very nice, can you also compare it to https://maki.sh?
Would be interesting to compare to a harness optimizing for cost reduction too.