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October 15, 2026Constellation · CEG · Vistra · VST5 min read

The first nuclear deal got a shrug. The second got 12%.

In the first week of October, Constellation Energy rose 17.9% and Vistra 20.5%. The demand story behind it was weeks old. What changed was who signed, and how big.

What happened

From September 30 to October 7, Constellation Energy (CEG) went from $254.02 to $299.59, up 17.9%. Vistra (VST) went from $138.35 to $166.72, up 20.5%.

Most of it came in two days. On Monday, October 5, Vistra rose 3.5%. On Tuesday, October 6, Constellation jumped 12.2% to $300.40 and Vistra rose another 10.8% to $160.50.

September 30 → October 7, 2026
One week, two nuclear stocks
+17.9%Constellation (CEG), $254.02 → $299.59
+20.5%Vistra (VST), $138.35 → $166.72
Oct 6The big day: CEG +12.2%, VST +10.8%
Daily closing prices

Both companies own nuclear power plants. That matters because of who is buying electricity right now. AI data centers need a lot of power, all the time, and they want it from sources that don't burn carbon. Nuclear plants run around the clock and emit none. There aren't many of them, and new ones take years to build. So the existing plants have become something the biggest tech companies want to lock up for decades.

The demand was already in the news

None of that was new in October. On September 18, CNBC reported that Anthropic and OpenAI were hunting for smaller data center deals to add AI capacity faster. More data centers, sooner, means more power, sooner.

Then on September 30, after the market closed, Constellation and Amazon announced a 20-year power purchase agreement. It adds 190 megawatts of nuclear capacity at the Calvert Cliffs plant in Maryland, supports more than $3 billion of investment, and extends the plant's operating life.

A 20-year contract with Amazon is the kind of news you'd expect to move a stock. Constellation rose 1.9% the next day, then slipped back. By October 2 it was at $257.49, barely above where it started.

Then the second deal landed

Over the weekend, the story picked up two more pieces.

On Saturday, October 3, CNBC reported that the US government would lend Vistra $4.2 billion to expand its nuclear output, with the announcement planned for Monday at Vistra's Ohio plant. The Department of Energy then announced the conditional loan. Vistra rose 3.5% on Monday and 10.8% on Tuesday.

On Monday night, reports said Alphabet was close to a nuclear power deal with Constellation. Early reports put it near $1 billion. By Tuesday it was done, and Constellation closed up 12.2%. Later coverage described it as a 20-year, $4.3 billion agreement for 890 megawatts, much of it squeezed out of plants Constellation already runs.

Constellation · two 20-year power deals
Same company, same kind of contract, one week apart
AmazonSep 30
190 MW
Calvert Cliffs, $3B+ investment
+1.9% CEG the next day
GoogleOct 6
890 MW
$4.3B, mostly from existing plants
+12.2% CEG that day
Sources: Yahoo Finance, Bloomberg, CNBC

Put next to each other, the two Constellation deals tell you a lot. Same company, same kind of contract, one week apart. The Amazon deal was 190 megawatts. The Google deal was 890. And the Google deal arrived in the same days the government put $4.2 billion behind nuclear power at Vistra. One big contract is a deal. A second, bigger one from another tech giant, plus federal money for a rival, looks like a market forming.

The other side

It wasn't one-way. On September 22, the Financial Times reported that US officials were moving to rein in utility profits as power bills rise. The question was how much of the money from data center demand should go to shareholders, and how much should go back to customers.

The app I build, Loom, links each news story to the stocks it's likely to affect, and it put that FT story next to both Constellation and Vistra. That's what made me read it as the other half of this week, not background.

The prices reflected that doubt. Through the second half of September, Constellation drifted from $262.80 to $254.02, and Vistra from $140.78 to $138.35. And the rally didn't hold in full. By October 14, Constellation was at $279.54, down 6.7% from its October 7 close, and Vistra at $151.79, down 9.0%.

Daily close, indexed to 100 on September 30
A September drift, an October jump, then some of it back
901001101201234Sep 21Sep 30Oct 7Oct 14
Constellation (CEG)Vistra (VST)
  1. 1Sep 22FT: officials move to rein in utility profits.
  2. 2Sep 30Amazon signs 20-year nuclear deal with Constellation (after the close).
  3. 3Oct 3–5$4.2B federal loan for Vistra reported, then announced.
  4. 4Oct 6Google deal with Constellation. CEG +12.2%, VST +10.8%.
Daily closing prices, Sep 21 – Oct 14, 2026

What I take from it

A theme being in the news isn't the same as a theme being priced. "AI needs power" had been a headline for months. What moved these two stocks was proof of scale: a second, larger contract, from a second tech giant, in the same week the government put money behind nuclear.

It's the other end of the AI build-out from CoreWeave, whose bonds broke the following week. The companies borrowing to rent out GPUs were being questioned. The companies selling the electricity were signing 20-year contracts.

Sources

Prices are daily closes. This is not investment advice.

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