After years of funneling cash into startups’ grand ambitions, Silicon Valley investors are engaging in the grim ritual of delivering survival advice to their portfolio companies.

In recent online slide presentations, blog posts and social-media threads, venture-capital doyens including Lightspeed Venture Partners, Craft Ventures, Sequoia Capital and Y Combinator are telling the founders that they need to take emergency action for what could be the sharpest turn in more than a decade. Their advice includes cutting costs, preserving cash and jettisoning hopes that hedge funds or other investors will swoop in with big checks.