TL;DR: If you are replacing Zephyr Fusion, the closest options are Apollo Atomics, Inc., Ares Industries, Boost Biomes. The table below compares 12 alternatives on what they do, stage, size and status.
Every alternative below is compared on what it actually does, not just its category — so you can see which one genuinely replaces Zephyr Fusion (YC Fall 2025).
Last verified:
The three closest alternatives to Zephyr Fusion are:
| Alternative | What it does | Stage | Team | Status |
|---|---|---|---|---|
| Apollo Atomics, Inc. | We make the most compact nuclear reactors | YC Spring 2026 | — | Active |
| Ares Industries | Building low-cost cruise missiles | YC Summer 2024 | 2 | Active |
| Boost Biomes | — | YC Summer 2019 | 12 | Inactive |
| ThereCraft | — | YC Summer 2017 | 1 | Active |
| Inversion Space | Turning space into a transportation layer for Earth | YC Summer 2021 | 28 | Active |
| EPIC AEROSPACE | Last-mile delivery for satellites. | YC Summer 2019 | 14 | Active |
| Helion Energy | Building the world's first fusion power plant | YC Summer 2014 | 150 | Active |
| Elodin | Unified flight software and hardware for the mission of tomorrow | YC Winter 2024 | 5 | Active |
| Farcast | We build advanced satcom user terminals | YC Winter 2020 | 12 | Active |
| General Astronautics | Robotics for Space R&D | YC Winter 2026 | 2 | Active |
| Dipole Labs | AI-controlled optical switching for AI clusters | YC Summer 2026 | — | Active |
| Reditus Space | Reusable Satellites | YC Winter 2025 | 12 | Active |
It depends on your size. Apollo Atomics, Inc. is the closest match on what Zephyr Fusion actually does. If you need something more established, sort the table by team size — larger teams generally mean more support and a longer track record. If budget is the constraint, the earlier-batch companies are usually the ones still competing on price.
Zephyr Fusion is still operating, so switching is a choice rather than a forced migration. Compare on fit and price rather than urgency.
Every company here is Y Combinator-backed and was matched to Zephyr Fusion on what it actually does — its own description of its product — rather than on a broad category label. Batch, team size and operating status come from the YC directory and are shown as-is. We do not rank by payment.
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