Mainspring Energy builds fuel-flexible, low-emissions linear generators for onsite power generation. Its systems are designed to provide dispatchable electricity with lower carbon and near-zero NOx emissions versus traditional backup generation.
Access to pre-IPO shares is available to accredited investors through UpMarket.
Latest Round
Series F
Apr 2025, $258M raised, per Mainspring Energy company press release and General Catalyst
Valuation
Not disclosed
No valuation reported by a reputable outlet
How to Invest in Mainspring Energy Through UpMarket
Mainspring Energy shares are not on public exchanges. UpMarket provides accredited investors access through secondary market transactions.
Step 01
Verify accredited investor status
Confirm eligibility under SEC Rule 501 of Regulation D. Income or net worth threshold applies.
Step 02
Create an UpMarket account
Complete KYC/AML onboarding. Typically 1–2 business days. Licensed rep assigned on signup.
Step 03
Review available Mainspring Energy offerings
Full offering memoranda and risk disclosures provided before any commitment is required.
Step 04
Complete subscription documents
Review and sign subscription agreement. All documents handled digitally through the platform.
Step 05
Fund your investment
Wire transfer or ACH. $50K minimum. Funds held in custodial account until close.
Pre-IPO investments are illiquid, speculative, and involve risk of total loss of capital.
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Valuation Growth Over Time
Post-money valuation by round
Previous roundsMost recent
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Why Investors Are Watching Mainspring Energy
Growth Signal
Mainspring adds six utility and data center leaders
Mainspring formed a Strategic Advisory Board with six senior leaders from utilities and data centers, including former Google and utility executives. The company says its linear generator is fully dispatchable and scales from 250 kW to 100+ MW, supporting larger deployments.
Product Milestone
California CEC cites Mainspring's ultra-low-emission tech
A California Energy Commission report describes Mainspring's linear generator as using a low-temperature air-and-fuel reaction to drive magnets through copper coils. The report frames the system as high-efficiency and ultra-low-emission, underscoring product differentiation.
Market Opportunity
Data-center power demand creates opening for local generation
Mainspring says surging grid demand from the data-center boom is increasing interest in customer-sited power that can be affordable, reliable, and sustainable. Latitude Media reports the company is building a massive data-center pipeline, even as federal funding uncertainty remains a factor.
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No. As of March 2026, Mainspring Energy is a private company and does not trade on any public stock exchange. Accredited investors can access Mainspring Energy shares through UpMarket, a FINRA-registered broker-dealer that specializes in pre-IPO investments.
Mainspring Energy 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 Mainspring Energy 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 alternative investments since 2019.
Pre-IPO investments carry significant risks. Mainspring Energy 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.
Mainspring Energy builds fuel-flexible, low-emissions linear generators for onsite power generation. No valuation has been reported by a reputable outlet.