$IREN: H2 Root Cause Analysis Update I got more information tonight confirming that the issue stems from either MSFT AI model research team not communicating workload requirements to MSFT HPC systems team or that MSFT HPC team incorrectly translated those workload requirements to networking requirements. MSFT HPC systems team communicates the requirements to IREN and defines the acceptance tests. The miss was both in specs provided to IREN and acceptance test for H1. This is not an error discovered while bringing up the network core to combine H1 and H2. Yes if IREN had a principal networking engineer with deep knowledge of AI workload requirements, they could have prevented this but it's MSFT's responsibility to give the the full requirements as they own the model and platform layers. Expectation is that H1 continues billing and new specs are implemented as maintenance over a 4 months. For H2, this is a design change that IREN has to respond to which will incur a 45 day delay. H3 is not most cabled at all so will not be delayed as much and be delivered at the same time as H4. H4, not cabled at all, will incur no delay and be delivered in Dec. H1-4 will all be billing exiting 2026. For those wondering why cabling can result in a 45 delay and worrying that a 45 day must mean structural changes in liquid cooling or power distribution, you can watch this youtube video to understand how time consuming cabling can be. Credits to @pietrovl on good video pointing out how complex cabling can be. Most likely, IREN is still using MPO since EBO came out just this July and hard to supply chain.