Sierra, the AI startup co-founded by OpenAI chairman Bret Taylor, has raised $175 million in a funding round that values the startup at $4.5 billion.

Sierra, launched by Taylor and longtime Google exec Clay Bavor, focuses on selling AI-powered customer service chatbots to brands like WeightWatchers and Sirius XM. There’s an “agent” component, as well. The platform connects to other enterprise systems to undertake tasks on behalf of the customer without humans being involved.

There’s certainly no shortage of competition in the chatbot space. But Sierra claims its tech is less susceptible to hallucinations, the made-up facts AI models occasionally spew.

Sierra also lets customers customize its AI’s personality to their corporate brand, using a “constellation” of generative AI models from OpenAI, Anthropic, and Meta, among others, to complete tasks and check for accuracy.

Taylor and Bavor have a long history in customer service tech. Taylor spent nearly a decade at Salesforce, and years ago founded Quip, which Salesforce bought for $750 million in the summer of 2016. Bavor managed Gmail and Google Drive at Google, among other consumer-facing products.

Taylor met Bavor while at Google, where he worked before serving as Facebook’s CTO for several years. At Google, Taylor is widely credited with helping to launch Google Maps. Years later, he’d oversee the Twitter board throughout the social media site’s takeover by Elon Musk.

Investors in Sierra’s latest round included ICONIQ and Thrive Capital. Greenoaks Capital led the round, which brings Sierra’s total raised to $285 million, per Crunchbase.

TechCrunch has an AI-focused newsletter! Sign up here to get it in your inbox every Wednesday.