Sam Altman’s OpenAI exit leads to rollercoaster for sector

Firing of industry figurehead led to rebellion at his former employer and his hiring by its rival Microsoft

• OpenAI staff threaten mass walkout unless Altman is reinstated

The blog headline was anodyne – “OpenAI announces leadership transition” – but the consequences for Silicon Valley were seismic.

On Friday the company behind the hit AI text-generating system ChatGPT announced that Sam Altman, figurehead for the business and the artificial intelligence revolution that has enthralled and alarmed the world in equal measure, had been fired as chief executive.