IBM says changing only the agent harness moved one model from 30% to 81% of tasks
IBM Research published a comparison on 3 November 2026 that held the model fixed, the open-weight GLM-5.3-flash, and changed only the harness: the loop that plans, calls tools and checks results around a model. On AppWorld, a benchmark of multi-step tasks across 9 apps and 457 APIs, IBM says its own CUGA harness passed 73 of 90 tasks (81%), Nous Research's Hermes passed 42 (47%) and LangChain's Deep Agents passed 27 (30%).
Why it matters: Most vendor evaluations ask which model to buy. IBM's result says the wrapper may move the outcome as much as the model does. If you are choosing between agent platforms that all run the same underlying model, the platform is a real decision, not packaging.
The catch: IBM wrote the post and sells the winner. It concedes a 90-task sample on one benchmark, and that the setups were not identical: CUGA got AppWorld-specific instructions, while Hermes ran its default setup and Deep Agents needed two fixes so malformed replies did not end runs. IBM also says neither rival was built for multi-app API work. It reports no cost per task and no latency.
Zoom out: IBM credits the gap to showing each step only one app's tools instead of all 469, running model-written code in a time-limited sandbox, and checking each code block that changes data before it runs. The post also argues that rules in a system prompt are instructions, not enforcement. In IBM's demo, an agent with no policy paid $90 for "Pay everything I owe", including a denied claim; one with a policy held the payment for approval and paid the $10 due. That is one demo.
What to do: Fix the model, then run two or three harnesses on 30 of your own tickets or workflows, counting a case as passed only if three repeat runs all pass. Move any hard limit, such as a payment ceiling or an approval step, out of the prompt and into code that runs before the tool does.
Our coverage →IBM Research on the Hugging Face blog: CUGA harness comparison on AppWorld (vendor-published) ↗