Braintrust

AI agent testing in 2026 requires a fundamentally different approach than traditional software QA: because agents plan, call tools, and adapt across multiple steps, you must evaluate the entire decision trajectory — not just the final output. This guide walks through the complete evaluation stack, from golden dataset construction to CI/CD deployment gates. Why Traditional Software Testing Breaks for Multi-Step AI Agents Traditional software testing assumes deterministic, predictable behavior: given input X, the function reliably returns Y. Multi-step AI agents violate this assumption at every layer. An agent doesn’t just map inputs to outputs — it perceives context, selects tools, interprets intermediate results, adjusts its plan, and eventually produces an answer through a sequence of decisions that can vary on every run. As of 2026, 79% of organizations have adopted AI agents to some extent, and 57% already have agents in production (Multimodal.dev). Yet over 40% of agentic AI projects are at risk of cancellation by 2027 if governance, observability, and ROI clarity are not established (Gartner). The root cause is almost always testing inadequacy — teams apply unit-test thinking to systems that require trajectory evaluation. A unit test catches a wrong return value; what it cannot catch is an agent that reaches the right answer through a broken series of tool calls that would fail at scale or under edge-case inputs. ...

The fastest-moving part of AI infrastructure in 2026 is observability — and for good reason. The LLM observability platform market hit $2.69B this year (up from $1.97B in 2025), growing at a 36.3% CAGR. Three platforms dominate production use: Braintrust (SaaS-only, $80M Series B, enterprise-grade CI/CD gates), Arize Phoenix (100% open-source, OpenTelemetry-native, 9,100+ GitHub stars), and Langfuse (MIT-licensed, ClickHouse-acquired, 19,000+ GitHub stars). Choosing the wrong one means either paying for features you won’t use or hitting invisible ceilings when your agent fleet scales. ...

In 2026, choosing the wrong LLM evaluation tool is as costly as shipping bad code. The LLM observability market hit $2.69 billion this year and is projected to reach $9.26 billion by 2030. Gartner estimates that 50% of all GenAI deployments will rely on LLM observability platforms by 2028. Three tools dominate the conversation: DeepEval, a Python-native open-source framework with 14 built-in research-backed metrics; Braintrust, a production monitoring and eval lifecycle platform fresh off an $80M Series B at an $800M valuation; and PromptFoo, a security-focused testing tool that OpenAI acquired in March 2026. Each solves a genuinely different problem, and picking the right one depends entirely on where your evaluation gaps actually are. ...

Braintrust is a unified AI observability and evaluation platform that combines LLM tracing, dataset curation, prompt management, and automated evals in one product. After running it across three production LLM applications over six months, it’s the most complete end-to-end evaluation toolchain available in 2026 — but it comes with real trade-offs worth understanding before committing. What Is Braintrust? The AI Observability Platform Explained Braintrust is an AI observability platform that covers the full LLM development lifecycle: capturing production traces, running automated evaluations against datasets, managing prompts with version control, and feeding results back into CI/CD pipelines to block regressions. Founded in 2023 and backed by $242.5M across seven funding rounds — including an $80M Series B in February 2026 led by ICONIQ at an $800M valuation — Braintrust has positioned itself as the “observability layer for AI.” The company’s core thesis is that LLM applications need fundamentally different tooling than traditional software monitoring: AI traces average ~50KB per span versus ~900 bytes in conventional observability, queries involve semantic similarity rather than exact matching, and quality regressions are probabilistic rather than binary. To handle this, Braintrust built Brainstore, a purpose-built columnar database that achieves 80x faster queries than traditional data warehouses on AI workloads, with median query times under one second on real-world datasets. Enterprise customers include Notion, Stripe, Vercel, Airtable, Instacart, Zapier, Ramp, Dropbox, Cloudflare, and BILL — a roster that signals product-market fit at scale. ...