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Sierra

What Sierra does

Sierra (sierra.ai) is an enterprise customer-experience (CX) platform for building and operating “AI agents” that can handle complex, multi-step customer journeys across channels (voice, chat, email, messaging, and ChatGPT). Rather than deploying single-use support bots, Sierra positions its agents as relationship-driving systems that can pursue longer-horizon goals (spanning days or months) and execute actions by connecting to enterprise systems of record. The company highlights an “outcomes-based” approach to pricing, aiming to align cost with the value delivered by the agent. Sierra’s platform includes tooling for agent building (Agent Studio), agent runtime/orchestration (Agent OS / “Horizon”), knowledge grounding and context management (Context Engine and related capabilities), continuous evaluation and optimization (Insights and Explorer), and multimodal channel support (including Voice Personas and multimodal conversation experiences).

News

Company record

Sep 10, 2026 · Official · SierraNext gen multimodal agents: an interface that morphs with the conversation

Sierra described an update to multimodal agent experiences that bring voice, text, and visuals into the same conversation, explaining how teams can decide which medium to use when.

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Sep 08, 2026 · Official · SierraHyper-𝜏-bench: Evaluating agents that build agents (open-sourcing)

Sierra announced it is open-sourcing hyper-𝜏-bench (published as 𝜏^𝜏-bench), describing it as a long-horizon agent evaluation for models that can construct agents.

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Sep 04, 2026 · Official · SierraAI for call centers: an operating and rollout guide

Sierra published an enterprise guide framing rollout of AI in call centers as an operating-model change, covering routing, workforce, controls, failover, and expansion.

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Sep 01, 2026 · Official · SierraWhat is voice AI? An enterprise guide to AI voice agents

Sierra published an enterprise guide to voice AI and describes evaluation dimensions for enterprise voice agent readiness such as hearing, latency, action, guardrails, and handoff.

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Aug 31, 2026 · Official · SierraJulia Brau Donnelly joins Sierra as Chief Financial Officer

Sierra announced Julia Brau Donnelly’s appointment as Chief Financial Officer.

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Aug 25, 2026 · Official · SierraSophisticated agents for the most demanding companies: Sierra launches in Korea (Seoul office)

Sierra announced opening an office in Seoul and described its positioning for complex enterprises and measurable outcomes.

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Aug 20, 2026 · Official · SierraRelease governance: guardrails for agents at scale

Sierra described “release governance” as a set of checks, approvals, and rollout strategies to move agent changes safely from builder environments to live customer conversations.

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Aug 14, 2026 · Official · SierraBuilding in Germany, Austria and Switzerland (Munich office)

Sierra announced opening an office in Munich to support its presence across Germany, Austria, and Switzerland.

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Show 4 earlier updates
Aug 07, 2026 · Official · SierraIntroducing Voice Personas

Sierra announced Voice Personas, positioned as a way to design how an agent expresses itself (voice and personality) for brands, and described additions to agent SDK capabilities for voice behavior during real conversations.

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Jul 23, 2026 · Official · SierraWe’re excited to share that Sierra is acquiring Takeoff

Sierra announced it is acquiring Takeoff and described Takeoff as building a long-horizon agent runtime and contributing to the development of Horizon.

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Jul 16, 2026 · Official · SierraThe next Horizon in agents

Sierra described Horizon as its long-horizon agent capability for orchestrating outbound and inbound interactions over days or weeks, emphasizing context and long-horizon planning.

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May 04, 2026 · Official · SierraBetter customer experiences. Built on Sierra (Sierra raises $950M)

Sierra announced it is raising $950 million led by Tiger Global and GV at a valuation of over $15 billion, describing investment plans for platform, US growth, and international expansion.

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Source map · 2 recurring channels · 46 references
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Still resolving: Newsroom · Official X

Funding

Latest disclosed valuation$15B
Tracked capital$1.8B5 sourced rounds
DateRoundRaisedValuationLead / investorsEvidence
May 04, 2026Series E$950M$15B
Sep 04, 2025Series C$350M$10B
Oct 29, 2024Series financing (reported)$175M$4.5B
Oct 28, 2024Series B$175M$4.5B
Feb 13, 2024Seed$110M$1B
Not attributed
+2 investors

What it builds

Agent Studio

Agent Studio is Sierra’s “no code required” tooling for CX teams to build and manage agents using journeys, knowledge sources, integrations to systems of record, simulations/regression testing, and branding/controls such as voice and experience personalization.

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Horizon

Horizon is Sierra’s long-horizon agent capability designed to carry out complex outcomes over days or months, coordinating signals, playbooks, consent-aware delivery, and persistent customer context to drive end-to-end workflows.

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Ghostwriter

Ghostwriter is positioned as an “agents as a service” / agent-building experience that creates and optimizes agents by describing what the agent should do, targeting deployment-ready customer experiences with guardrails.

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Context Engine

Sierra’s Context Engine is described as the component that connects agents to customer relationship data and signals (spanning CRMs, data warehouses, and systems of record) so decisions can be tailored to each customer across interactions and over time.

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Insights

Insights provides reporting, experimentation, and observability for agent performance and business impact, including key metrics (for example CSAT and resolution), investigation workflows, conversation design experimentation, and monitoring/auditing of agent actions.

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Explorer

Explorer is Sierra’s “agent-optimizing agent” that continuously delivers insights in the background, supports deep research-style investigation over customer conversations, and generates actionable recommendations that can be sent to Ghostwriter for implementation.

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Channels

Channels is Sierra’s multi-channel deployment capability for building once and deploying across voice, messaging, email, Live Assist (care representative assist), and publishing to ChatGPT apps, with channel-specific capabilities and controls.

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Trust and reliability

Sierra’s trust and reliability product area describes governance, compliance, and security posture, including claims about not using customer data to train models and supporting enterprise security standards.

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Key metrics

Milestones & partnerships