For example, consider something like SWEBench, where a test should pass. Harness or a skill can just tell the agent keep trying until the test pass. So same model can have a lot of behavior changes between the harnesses.
In my experience (i own a multi-agent IDE with 50+ supported harness) folks stick to first party, usually either openai or anthropic, grok, agy; if they are willing to pay for the subscription the value is unbeatable. And they don't risk trying different harnesses.
For example, consider something like SWEBench, where a test should pass. Harness or a skill can just tell the agent keep trying until the test pass. So same model can have a lot of behavior changes between the harnesses.
In my experience (i own a multi-agent IDE with 50+ supported harness) folks stick to first party, usually either openai or anthropic, grok, agy; if they are willing to pay for the subscription the value is unbeatable. And they don't risk trying different harnesses.