Carbon13 has launched Carbon13 SEIS Fund X, its tenth SEIS fund since 2021, offering exclusive rights to invest in startups built through its Venture Builder in Cambridge. The fund invests across the climate horizontal, spanning energy, AI, materials, food security, supply chain resilience, and related sectors.
Managed by SyndicateRoom, the fund offers investors 50% SEIS income tax relief, tax-free gains on growth, 50% capital gains tax relief on the sale of other assets, and full Business Property Relief outside the new £2.5 million cap introduced in April 2026. Carry back of income tax relief to 2025/26 is available.
The fund is the only SEIS fund with a 12-month portfolio support programme designed to maximise startup graduation success. Carbon13's Venture Builder draws on an ecosystem of domain experts, investor partners, scientific advisors and industry partners across the UK and Europe.
Global climate tech venture and growth investment reached $40.5 billion in 2025, up 8% year-on-year, bringing cumulative investment since 2020 to $255 billion. At the deployment layer, global energy transition investment reached a record $2.3 trillion.
Carbon13 has invested in 107 ventures since 2021 across the UK and Europe. Portfolio companies have raised more than £50 million in follow-on capital, on top of the initial £13 million deployed by Carbon13. Notable portfolio companies include Cocoon Carbon, which raised a $15 million Series A in March 2026 at a post-money valuation of $54 million - representing an 8.68x MOIC on entry - to decarbonise steel and cement; MatNex, an AI materials discovery platform; Textrax, an AI platform for energy infrastructure; and Nanoplume, a superinsulator materials company. The Carbon13 portfolio has a potential emissions reduction of 450 million tonnes of CO2e per year when at scale.
In 2026 the bar is raised for pre-seed investors, the mix of opportunity and uncertainty means that it's more important than ever that founders are getting their go-to-market strategies right first time. It's not just about who has capital to deploy, but how they can support the founders post investment. Top founders are looking for investors who are industry connectors for pilots and investment, referrers for key first hires, conduits for innovation, participants in follow-on rounds, true partners for success. All things Carbon13 was built to do. The Carbon13 SEIS Fund X has exclusive access to all that value.
Institutional capital moving upmarket is rational - but it widens the gap at exactly the stage where the opportunity is sharpening. Less competition for the best early teams, more disciplined entry valuations. Add the April changes to Business Property Relief, and we're seeing advisers look at SEIS with fresh eyes. The combination is more compelling than it's been in a while.
