[schnitzelstoat]

But now instead of spending 10 hours working on that, he can go and work on something else that would otherwise have required another engineer.

It's not going to mean they can employ 0 engineers, but maybe they can employ 4 instead of 5 - and a 20% reduction in workforce across the industry is still a massive change.

[bodge5000]

Thats assuming a near 100% success rate from the agent, meaning it's not something he needs to supervise at all. It also assumes that the agent is able to take on the task completely, meaning he can go do something else which would normally occupy the time of another engineer, rather than simply doing something else within the same task (from the sounds of things, it was helping with debugging, not necessarily actually solving the bug). Finally, and most importantly, the 20% reduction in workforce assumes it can do this consistently well across any task. Saving 10h on one task is very different from saving 10h on every task.

Assuming all the stars align though and all these things come true, a 20% reduction in workforce costs is significant, but again, you have to compare that to the cost of investment, which is reported to be close to a trillion. They'll want to see returns on that investment, and I'm not sure a 20% cut (which, as above, is looking like a best case scenario) in workforce lives up to that.