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This is a weekly feature that runs down the week’s top 10 announced funding rounds in the U.S. Check out last week’s biggest funding rounds here.

Usually, as December wears on, startups announce fewer and fewer big rounds. However, that was not the case this week, as five companies announced rounds of $100 million or more. Pretty good for what is normally a quiet time of year.

1. X.AI, $135M, artificial intelligence: You may have heard Elon Musk has an artificial intelligence startup to compete with OpenAI. Well, this week it was reported by various sources the company, X.AI (of course), is attempting to raise $1 billion, per a securities filing earlier this week. So far, the Austin, Texas-based company has raised $135 million. Musk was a co-founder in OpenAI, so AI is not new to him. X.AI was announced in July — funded by Musk himself —  and released an early version of its ChatGPT competitor, Grok, last month.

2. Seismic Therapeutic, $121M, biotech: Cambridge, Massachusetts-based Seismic Therapeutic led the way for biotechs this week — although it is far from the only biotech on this list. The machine-learning immunology company closed a $121 million Series B led by new investor Bessemer Venture Partners. The new cash will be used to further push the trials of two therapies for different types of autoimmune diseases. Last year Seismic raised a  $101 million series A round. Founded in 2020, the company has now raised $222 million, per Crunchbase data.

3. Vast Data, $118M, data: AI data platform startup Vast Data raised a $118 million Series E led by Fidelity Management and Research Co., jumping the company’s valuation to $9.1 billion. The new valuation is a significant spike from its previous valuation of $3.7 billion set in 2021. Vast’s data storage platform is optimized for AI workloads across datacenters and clouds, allowing customers to manage both structured and unstructured data to generate insights. The New York-based company already has seen significant growth. At the end of its fiscal year third quarter, Vast Data had surpassed $1 billion in cumulative software bookings — a 3.3x year-to-year growth rate. It also maintained positive cash flow for the last 12 quarters. This is not the first headline-grabbing move for Fidelity Management and Research this week. Earlier in the week it led a $642 million minority investment in AI cloud infrastructure company CoreWeave — which saw its valuation hit $7 billion. The new valuation — as reported by Bloomberg — is a significant jump from late May, when the company extended its Series B at a $2 billion valuation. Founded in 2016, Vast has raised $381 million, per Crunchbase.

4. Odyssey Therapeutics, $101M, biotech: Just about 13 months ago, Boston-based Odyssey Therapeutics led this list when it locked up a $168 million Series B led by General Catalyst. It’s back this week after it closed a $101 million Series C led by Ascenta Capital. Odyssey is developing precision immunomodulators and oncology medicines to treat serious human diseases, and has a portfolio of immunology and oncology therapeutics. Founded in 2021, Odyssey has raised nearly $487 million, according to the company.

5. Gecko Robotics, $100M, robotics: Gecko Robotics became the latest startup in defense tech to make waves with a big raise in recent weeks. The company,  which creates robots to assess the safety and condition of critical infrastructure, raised an additional $100 million in a Series C extension led by some big names — the US Innovative Technology Fund and Founders Fund.  The Pittsburgh-based robotics startup announced a $73 million Series C in March 2022. The new round comes a month after the startup landed a contract with the U.S. Navy to use its robots to assess damage as it builds submarines. Founded in 2013, the company has raised $222 million to date, per Crunchbase data. The round is the latest big round to go to a defense tech startup as VCs start to seemingly warm to the industry. However, just last week rocket propulsion startup Ursa Major said it has added another $38 million to its previously reported $100 million Series D — bringing its total Series D and D-1 funding to $138 million. In October, defense and aerospace startup Shield AI raised a massive $200 million Series F at a $2.7 billion valuation.

6. (tied) Artbio, $90M, biotech: Cambridge, Massachusetts- and Switzerland-based clinical-stage radiopharmaceutical company Artbio closed a $90 million Series A co-led by Third Rock Ventures and an undisclosed health care fund. Founded in 2021, the company has raised $113 million, per Crunchbase.

6. (tied) Cortex, $90M, health care: Menlo Park, California-based Cortex, a medical technology company treating atrial fibrillation, launched and raised $90 million in funding led by KKR and Hellman & Friedman.

8. X-energy, $80M, energy: Rockville, Maryland-based X-energy, a developer of advanced small modular nuclear reactors and fuel technology, completed its Series C financing with an additional $80 million from Ares Management Corp. and Kam Ghaffarian. This additional cash brings the total capital raised in the Series C financing round to $235 million.

9. Pontera, $60M, fintech: New York-based Pontera, the fintech company enabling 401(k) participants to receive wealth management services, secured $60 million in a funding led by Iconiq Growth. Founded in 2021, Pontera says it has raised $160 million.

10. (tied) AssemblyAI, $50M, artificial intelligence: San Francisco-based AssemblyAI, which builds speech Al models, raised a $50 million Series C led by Accel. Founded in 2017, AssemblyAI has now raised $115 million, per the company.

10. (tied) MaintainX, $50M, asset management: San Francisco-based MaintainX, a provider of a maintenance and frontline work execution platform, raised $50 million in funding led by Bain Capital Ventures. Founded in 2018, MaintainX has raised $104 million, per the company.

Big global deals

The biggest raise of the week came from South America.

• Brazil-based Emergent Cold Latin America, a refrigerated warehousing and logistics provider, raised a $500 million venture round.

Methodology

We tracked the largest announced rounds in the Crunchbase database that were raised by U.S.-based companies for the seven-day period of Dec. 2 to Dec. 8. Although most announced rounds are represented in the database, there could be a small time lag as some rounds are reported late in the week.

Illustration: Dom Guzman