Why SMR capital is flooding in now
13+ announced hyperscaler-nuclear deals had committed over 9.8 gigawatts of capacity to AI data center infrastructure as of May 2026, with every major U.S. hyperscaler signing at least one. That demand — not climate policy — is the real driver behind the current wave of SMR capital.
That pattern shows up directly in this list: Amazon anchored X-energy's Series C-1 and now has an offtake right on its first Xe-100 plant. Google struck a Master Plant Development Agreement with Kairos Power for a 500 MW fleet. Meta signed separate deals with both Oklo (1.2 GW in Ohio) and TerraPower (up to eight Natrium reactors). None of these are speculative climate bets — they're power-purchase commitments tied to specific data center buildouts, which is why the capital keeps arriving even as first-power dates for most of these plants still sit years out. For the broader AI-compute demand curve behind all of it, see our Moore's Law dashboard.
The field — five companies, five reactor designs
Two public, three private · none generating commercial power yet| Company | Status | Valuation | Reactor | Key backers |
|---|---|---|---|---|
| Oklo | Public — NYSE: OKLO (SPAC merger closed May 2024) | ~$8.2B market cap (Aug 25, 2026) | Aurora — 15 MWe fast fission microreactor, recycled/fresh fuel | Sam Altman (chairman); merged via AltC Acquisition Corp SPAC |
| Kairos Power | Private — DOE-backed demonstration program | Undisclosed | Hermes / Hermes 2 — fluoride salt-cooled high-temperature reactor (molten salt) | U.S. DOE (up to $303M milestone-based Technology Investment Agreement); Google (Master Plant Development Agreement) |
| X-energy | Public — Nasdaq (IPO priced Apr 24, 2026) | ~$12B (post-IPO trading, Apr 2026) | Xe-100 — 80 MWe helium-cooled, TRISO-X pebble-fuel high-temperature gas reactor | Amazon (Climate Pledge Fund led ~$500M Series C-1, Oct 2024 — 2 board seats + first-plant offtake right); Laurene Powell Jobs |
| TerraPower | Private | Undisclosed | Natrium — 345 MWe sodium-cooled fast reactor with molten-salt energy storage | Bill Gates (founder); U.S. DOE (~$2B committed to licensing/construction/demonstration) |
| Valar Atomics | Private (Series B closed Aug 3, 2026) | $6B (tripled from $2B in months) | Ward 250 — modular fission reactor purpose-built to power AI data centers | Sequoia Capital (led $1B Series B); Atreides Management, Point72, Snowpoint Ventures; $200M credit facility |
Oklo: Excavation underway at Aurora-INL (Idaho); targeting 2028 startup. Signed Jan 2026 deal with Meta for a 1.2 GW nuclear campus in Ohio. Raised ~$1.85B net selling stock in H1 2026 to fund the first plant; total build cost undisclosed, still negotiating with contractor Kiewit. — Source: stockanalysis.com (Aug 25, 2026); implicator.ai; Fool.com
Kairos Power: Hermes 2 broke ground in Oak Ridge, TN — the first Gen IV power-producing reactor to receive an NRC construction permit. First deployment under Kairos' Google deal targeting a 500 MW fleet by 2035. — Source: World Nuclear News; ORNL/DOE press release; Kairos Power
X-energy: IPO raised ~$1.1B at $23/share. Amazon/X-energy target 5+ GW of Xe-100 capacity online in the U.S. by 2039 — the largest announced commercial SMR deployment plan to date. — Source: ESGToday; Carbon Credits; TechCrunch (Feb 2025 Amazon round)
TerraPower: NRC issued a construction permit in early 2026 — the first the NRC has ever granted for a commercial non-light-water power reactor. Construction underway at Kemmerer, WY; plant targeted for completion around 2030. Jan 2026 deal with Meta for up to 8 Natrium reactors, first two targeted online by 2032. — Source: DOE / NRC press release; GeekWire; Power Engineering
Valar Atomics: Ward 250 reached self-sustaining criticality in June 2026, then generated electricity to power an Nvidia Blackwell chip a week later — the first time an advanced reactor has directly powered AI infrastructure. — Source: Axios Pro Climate Deals (Aug 3, 2026); TechFundingNews
Licensing is the real bottleneck, not capital
Every company on this list has more capital than it can currently deploy — the constraint is the Nuclear Regulatory Commission's construction-permit process, which has approved exactly two non-light-water commercial designs in NRC history: TerraPower's Natrium and Kairos Power's Hermes 2, both in early 2026. Oklo's Aurora and X-energy's Xe-100 are earlier in that process. That licensing lag is why even fully-funded companies like TerraPower (backed by a ~$2 billion DOE commitment) and Kairos Power (a $303 million DOE technology investment agreement, plus Google as a fleet customer) still target first commercial power years out — Natrium around 2030, Hermes 2's commercial follow-on later in the decade.
Oklo is the starkest illustration of the capital-vs-construction gap: it's a $8.2 billion public company that has not generated a watt of commercial power and hasn't published a total cost for its first plant. That's the bet every investor in this sector is making — that regulatory approval and construction execution catch up to the offtake demand that's already been signed.
Standard Nuclear — the microreactor IPO
Standard Nuclear isn't in the comparison table above because we've already covered it in depth as a public microreactor stock story, separate from this private/pre-revenue cohort. Read the full breakdown and the post-IPO performance update.
Go deeper on Valar Atomics
Valar's $1 billion Sequoia-led Series B — a $6 billion valuation, tripled in months — is the newest and largest single SMR round in this tracker. Full deal terms and context in our deep dive.
Valar Atomics: $1B Series B at $6B valuation →Nuclear SMR investing — common questions
What is a small modular reactor (SMR)?
An SMR is a nuclear fission power plant designed at a fraction of the size of a traditional reactor — typically 15 to 300 megawatts versus 1,000+ MWe for a conventional plant — built from factory-manufactured modules instead of poured on-site. Smaller size means lower upfront capital, faster construction, and siting options (like next to a data center) that a gigawatt-scale plant can't match.
Which SMR company has the highest valuation?
X-energy, at roughly $12 billion after its April 2026 Nasdaq IPO. Valar Atomics is close behind at a $6 billion private valuation after its August 2026 Sequoia-led Series B, and Oklo trades on the NYSE at a market cap of roughly $8.2 billion as of late August 2026. Kairos Power and TerraPower are both private and have not disclosed valuations.
Why are SMR startups raising so much capital right now?
AI data center power demand, not climate policy, is the proximate driver. As of May 2026, 13+ announced hyperscaler-nuclear deals had committed more than 9.8 gigawatts of capacity to AI infrastructure, and every major U.S. hyperscaler — Amazon, Google, Meta, Microsoft — has signed at least one. Data centers need firm, 24/7, carbon-free power at a scale wind and solar plus batteries can't reliably deliver on the timelines hyperscalers want, and nuclear is the alternative getting funded.
Which SMR startups are actually under construction, not just planned?
Two have NRC construction permits and active builds: TerraPower's Natrium reactor in Kemmerer, Wyoming (the first NRC construction permit ever issued for a commercial non-light-water reactor), and Kairos Power's Hermes 2 in Oak Ridge, Tennessee (the first Gen IV power-producing reactor to receive one). Oklo's Aurora-INL site in Idaho is in excavation, targeting a 2028 startup. X-energy and Valar Atomics are earlier — X-energy is still pre-construction on its first commercial Xe-100 unit, while Valar's Ward 250 has reached criticality in a demonstration setting.
Can retail investors buy shares in these nuclear startups?
Two are public: Oklo trades on the NYSE (OKLO) and X-energy trades on Nasdaq after its April 2026 IPO. Kairos Power, TerraPower, and Valar Atomics remain private, venture- and DOE-backed companies with no public listing — retail access would require a pre-IPO secondary marketplace, which carries real liquidity and price-discovery risk.