Arthur is a private AI performance company that helps enterprises monitor and measure machine-learning models. Its platform focuses on improving model accuracy, explainability, and fairness for production use. [1]
Access to pre-IPO shares is available to accredited investors through UpMarket.
Arthur shares are not on public exchanges. UpMarket provides accredited investors access through secondary market transactions.
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Pre-IPO investments are illiquid, speculative, and involve risk of total loss of capital.
| Date | Round | PPS (split-adj.) | Valuation |
|---|---|---|---|
| 2021 | Series B |
Arthur AI says its platform helps teams ensure reliable AI across the full lifecycle, including agents, GenAI, and traditional ML applications. The company’s core product claim is faster shipping of AI systems with reliability controls built in.
Arthur AI’s messaging targets organizations deploying agents and GenAI, a market segment expanding as companies move AI from experiments into production. The platform is framed as infrastructure for teams that need monitoring and reliability across multiple model types.
Search results for “Arthur” include pages about investor Arthur Rock, not only the private tech company Arthur AI, which can create confusion in diligence and sourcing. This ambiguity raises the risk of mixing company facts with unrelated biographical material.
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No. As of March 2026, Arthur is a private company and does not trade on any public stock exchange. Accredited investors can access Arthur shares through UpMarket, a FINRA-registered broker-dealer that specializes in pre-IPO investments.
Arthur does not have a public stock price because it is privately held. The most recent known share price comes from its last funding round. Pre-IPO share prices on the secondary market may differ from the last round price depending on supply, demand, and market conditions.
Yes. Accredited investors can indicate interest in Arthur shares through UpMarket by filling out the form on this page or creating an account at upmarket.co. All pre-IPO offerings are subject to availability and require a $50,000 minimum investment. UpMarket is a FINRA-registered broker-dealer and has brokered more than $500M in alternative investments since 2019.
Pre-IPO investments carry significant risks. Arthur shares are illiquid, meaning there is no public market to sell them quickly. There is no guaranteed exit timeline or return. The investment is speculative in nature, and investors should be prepared for the possibility of total loss. Valuations of private companies can fluctuate substantially between funding rounds. Investors should consult their financial advisor and review all offering documents before investing.
In a pre-IPO transaction, accredited investors purchase shares from existing shareholders (such as employees, early investors, or other holders) through secondary market platforms. The company itself does not issue new shares in these transactions. UpMarket facilitates these trades as a FINRA-registered broker-dealer, handling compliance, documentation, and settlement on behalf of both parties.
There are two primary exit paths for pre-IPO holdings: selling your shares on the secondary market to another buyer, or holding until the company completes an IPO or is acquired. Both paths are subject to transfer restrictions, company approval (right of first refusal), and market conditions. The timing of any exit is unpredictable, and investors should plan for a multi-year holding period.
The minimum investment for most pre-IPO offerings on UpMarket is $50,000. This amount may vary depending on the specific offering and share availability. There are no fees to create an UpMarket account or browse available investments. Investors only pay transaction-related fees when they complete an investment.
UpMarket's valuation estimate of is derived from a proprietary model that incorporates multiple data sources: funding round data (Caplight), revenue estimates (Sacra), secondary market pricing, and public company comparables. The model applies a private company discount to the public comp multiple to account for illiquidity and information asymmetry. This estimate is not investment advice and may differ substantially from the price at which shares actually trade.
Arthur monitors and measures machine-learning model performance to improve accuracy and explainability, positioning itself as a reliability platform for AI agents — accredited investors can access Arthur stock through UpMarket.