Twitter co-founder Jack Dorsey says his technology firm Block is laying off almost half its workforce because artificial intelligence (AI) "fundamentally changes what it means to build and run a company." "Within the next year, I believe the majority of companies will reach the same conclusion and make similar structural changes," he wrote in a letter to shareholders. The layoffs will mean headcount at the company - which owns Square, CashApp and Tidal - will fall to less than 6,000 from 10,000. Block has seen several rounds of layoffs since 2024 but this is the first time it has cited AI as the reason for redundancies and marks the latest in a series of major job cuts in the tech industry. At the end of January Amazon laid off 16,000 employees, having already cut 14,000 roles a few months earlier. In a subsequent call discussing financial results, Brian Olsavsky, Amazon's chief financial officer, said the company was looking at cost reductions elsewhere as it ramps up AI spending.…