Today, most agents are built with the help of other agents like Sierra's Ghostwriter. Yesterday, Sierra open-sourced hyper-𝜏-bench (published as 𝜏^𝜏-bench), a new long horizon agent evaluation that measures how well models can not only act as an agent, but construct one.

I'm excited to announce that Julia Brau Donnelly will be joining Sierra as our Chief Financial Officer. Julia has seen companies from almost every side: as an investment banker, a private-equity investor, an operator at Wayfair, and as CFO of Pinterest. That range of experience and adaptability is so valuable in an industry that is changing at a pace none of us have seen before. Most of all, Julia embodies our culture: low ego, high agency, and excited to roll up her sleeves to get the work done. And there’s a lot of building to do. Just two and a half years since launch, Sierra has become the leading customer-facing conversational AI platform. The business is growing much faster than even our most optimistic predictions, hitting $100M in ARR in just seven quarters and $200M in nine quarters. We now work with over 40% of the Fortune 50, one in three of the leading banks, five out of 10 of the largest healthcare companies in the world, and 25% of the IBEX 35. With the shift from one-and-done service agents to revenue-aligned long-horizon agents, the opportunity for Sierra just got much, much bigger. Julia — welcome to Sierra! @claybavor and I are so excited to have you on the team.

Today, Sierra’s launching Voice Personas, which enable you to give your agent not just a voice, but a personality. Voice AIs shouldn't sound the same. It's time to empower every company to define their own brand voice. And we had a ton of fun messing around, as you’ll see in the video.

At Sierra we are very proud to have partnered with @foxone to deliver an exceptional customer experience during one of the biggest moments in sports. FOX's coverage of the 2026 FIFA World Cup broke television records, with the Spain vs. Argentina Final becoming the most-watched soccer telecast in U.S. history averaging 39.8M viewers. Simultaneously, FOX One customer engagement increased 15–20x. Despite the unprecedented demand, the AI agent successfully contained 86% of customer conversations. Most importantly, the majority of customers who engaged with the AI agent received successful resolutions, and customer sentiment remained positive throughout the tournament — demonstrating the power of combining AI with a thoughtful customer experience strategy. A huge thank you to the team at FOX One for an incredible partnership and for proving what's possible when innovation and customer obsession come together. Looking forward to what's next.

Excited to share that BBVA launched Sierra's first long-running Horizon agent in just 30 days — from initial discussion to production. It’s now serving BBVA customers in both Spain and Argentina.  Deploying AI at this pace is truly remarkable for an organization operating at the scale of BBVA and a testament to the leadership of @bravoacin and the bank’s amazing technology teams. Customers come first is a core BBVA value. With Horizon agents, they can build deeper relationships that help grow their business. @claybavor and I are so grateful for our partnership.

Since January, @SierraPlatform has grown revenue >100%, while growing our engineering team <15%. Small, AI-native teams are more productive, cohesive, and fun. Here are some examples of how we work 🧵

Last month we introduced Horizon, which enables agents to pursue long-term goals like originating a loan or settling an insurance claim. Today, we're excited to announced our partnership with @Plaid so customers can now securely connect their bank accounts with agents built on Sierra. This not only enables people to make payments or verify their finances without leaving the conversation — the agent can then use that information to complete longer-running tasks like refinancing a loan. It's a big pivot beyond customer support, to agents that can drive revenue, proactively engaging over days, weeks or months to deliver meaningful business outcomes. Read more from me and @ Will Robinson below.

We recently posted about Pinecone, Sierra’s internal agent every employee uses for everything from writing code to GTM. Mihai wrote up how the Pinecone team designed the MCP service behind it, including nuanced issues like access control and context overload. Check it out:

I'm proud to announce our partnership with SoftBank, the leading telecommunications and IT operator in Japan, with decades-long relationships across all the major enterprises there. We share the same competitive intensity and ambition to help companies deliver better outcomes for their customers with AI. I'm excited to also have SoftBank as a customer across its flagship SoftBank and Y!mobile brands, as well as additional services operated by its group companies.

We wrote up how we've AI-pilled Sierra. The centerpiece is an AI agent named Pinecone that the whole company uses for everything from business analysis to writing code. Pinecone now generates 70% of our PRs and automates hundreds of tasks every day to quietly handle work no one explicitly prompted.

Sierra is raising $950 million from new and existing investors, led by Tiger Global and GV, at a valuation of over $15 billion. We now have more than $1 billion to invest in becoming the global standard for companies wanting to transform their customer experiences with AI. Two years ago, most of our customers’ agents were limited to support — tracking orders, troubleshooting devices, and resetting passwords. Fast forward to today, and AI agents built on Sierra are powering all parts of the customer life cycle, from purchase consideration to product discovery to retention and more. We are so excited for what’s ahead, and are deeply grateful to our customers and partners for being on this journey with us.

As coding agents have become the standard for developing software, we've transformed Sierra's engineering interview process to be AI-native. We've documented our lessons here, and very curious how others in the industry are navigating

I’m excited to announce that Sierra has acquired Opera Tech in Japan. Opera’s co-founders, Keita Morikawa and Kiyo Kunii, started the company with the simple idea that AI could help businesses deliver high-quality customer experiences at scale. We’re so excited to have them join us to lead Sierra in Japan.

Today, Sierra is releasing Ghostwriter, our agent for building agents. With Ghostwriter, you can create an AI agent for your customer experience — one that can chat, pick up the phone, speak dozens of languages, take action on your systems of record, and be protected with industry-leading guardrails — simply by having a conversation. No clicking, no forms, no menus. Codex and Claude Code have transformed how we build software, making it possible for software engineers to orchestrate and review the work rather than doing all the work themselves. We think the same transformation will happen for all software. Rather than every enterprise app having a web app for humans and an API for automation, every software platform’s UI will be an agent that can do the work on your behalf. I recorded a demo of my building and optimizing an agent with Ghostwriter so you can see how powerful and easy it is to use. It’s completely changed the way our early adopters build agents, and it’s changed the way I think about the software industry. Let me know what you think, and, if you’re interested in trying it out at your business, please reach out directly.