Arm Holdings (ARM) is set to join the NASDAQ-100 index, replacing Sirius XM (SIRI). This inclusion is expected to prompt forced index buying, benefiting ARM's stock performance. The announcement has already led to a 0.4% pre-market increase and new all-time highs for ARM. The stock has been super strong for the past two months, reaching new all-time highs today. The timing is seen as advantageous for Softbank and its CEO, Masayoshi Son.