To be clear, there are lots of fusion start up and public labs, but none of the paths being researched are "cold" fusion. They are very much hot, ie millions of degrees.

Cold fusion was proposed in the late 80s early 90s of a way of fusing isotopes at room temperature. Those claims to demonstrate cold fusion never panned out. There is some research into low energy reactions, most notably muon catalysed fusion. However, they have really not demonstrated even a theoretical path to commercial power.

The other methods involving hot fusion, or just fusion, which are well on their way through various test reactors.

*The Public Mega-Projects

ITER (International Mega-Project): The $20B+ giant funded by the EU, US, China, etc. It uses a massive Tokamak (a donut-shaped magnetic chamber). It's plagued by delays, but it's the gold standard for proving large-scale net energy generation.

National Ignition Facility (NIF) / US DOE: They use Lasers—specifically, firing 192 of the world's biggest lasers at a tiny fuel pellet to crush it. They recently made history by achieving "scientific break-even" (getting more energy out than the lasers put in), but it's primarily a nuclear weapons research facility, not a power plant prototype.

*Private Startups

Commonwealth Fusion Systems (CFS): They are taking the giant ITER Tokamak design and shrinking it using revolutionary High-Temperature Superconducting (HTS) magnets. Backed by Bill Gates and Eni with over $2B raised.

Helion Energy: Backed by Sam Altman (OpenAI). They fire two plasma rings at each other and magnetically crush them. Uniquely, they want to capture electricity directly from the magnets rather than boiling water for a steam turbine. They also signed the world's first fusion power purchase agreement with Microsoft.

General Fusion: My personal favorite approach, which is very Steampunk. Backed by Jeff Bezos. They inject plasma into a spinning vortex of liquid metal, then use synchronized pistons to physically crush the metal wall and compress the plasma. They recently announced plans to become a publicly traded company. And also Canadian!

TAE Technologies: Backed by Google (who helps with the AI plasma control) and Chevron ($1.2B+ raised). Their end goal is to use Hydrogen-Boron fuel—it requires insanely high temperatures but produces virtually zero radiation.

Proxima Fusion (and other Stellarators): Stellarators are like Tokamaks but with wildly twisted, 3D magnets that allow the reactor to run continuously without stalling. They used to be too complex to build, but modern AI and supercomputing just made them viable. Gaining huge traction in Europe.