Flash loans provide uncollateralized, atomic leverage that eliminates traditional capital constraints on arbitrage. We document that flash-loan arbitrage exhibits substantially higher concentration than capital-funded arbitrage, with the top ten participants capturing approximately 50\% of volume compared to 20\% for traditional arbitrageurs. This pattern arises because atomic execution creates option-like payoffs with limited liability but reveals complete strategy information when broadcast publicly. Intense competition induces selection into costly private routing channels requiring non-transferable technological infrastructure. Our findings show that eliminating capital constraints shifts the binding constraint to technological capability, generating concentration through infrastructure requirements rather than financial capacity.