Helion Energy is developing the Polaris fusion reactor at its facility in Everett, Washington. Microsoft signed a power purchase agreement with Helion in 2023 to purchase 50 MW of fusion power by 2028 — with Helion paying Microsoft $1 per megawatt-hour for every month the target is missed after 2028. In January 2025 Helion raised $425 million to scale commercialisation, bringing total funding to over $2.2 billion. Helion uses a field-reversed configuration approach with deuterium-helium-3 fusion targeting commercial viability by 2028. CEO David Kirtley is backed by Sam Altman (OpenAI CEO) who personally invested $375 million in a 2021 round.