A story-driven MOD centered on exploration and investigation surrounding the alien-made giant submarine known as the Prototype.
Unknown technologies, sealed facilities, and the reactivated “Xeno-Leviathan” await the player.
This MOD allows the player to construct and pilot the Prototype, a massive alien-made submarine.
In its initial state, the Prototype has lost many of its functions, making it difficult to navigate dangerous waters as it is.
However, by investigating the Prototype-related facilities hidden throughout the crater,
the player can obtain upgrades that expand its capabilities, including self-repair, stealth systems, small-vehicle deployment, and warp functions.
As the player explores the alien facilities left throughout the crater,
they gradually approach the truth behind the mysterious Dead Zone Mapping Initiative that was once underway.
What was the purpose of this project? What is hidden within the Dead Zone?
And who is the entity calling out to the player through the automated systems?
Eventually, the player must confront the true mission hidden within the Prototype.
A grand journey awaits, expanding from the facilities within the crater to the unknown reaches of the Dead Zone.
A massive submarine with a unique structure, built on alien technology.
It serves as the central vessel in this MOD’s story progression, and its functions can be expanded through various upgrades.
2. 異星技術による追加装備・特殊アイテム群
2. Additional Equipment and Special Items Based on Alien Technology
Numerous new items are added, including alien-derived materials, equipment, and special devices.
These broaden exploration and progression, offering a fresh gameplay experience unique to this MOD.
Facilities related to the Prototype project exist across the crater, sealed away and isolated from the outside.
Use the clues provided by the Construction Terminal to uncover their locations and roles.
A gigantic alien-made machine operating autonomously deep underground.
Its precise functions and purpose remain unknown, and constant caution is required during exploration.
The exploration surrounding the Prototype eventually converges on a mysterious plan left behind by the aliens.
Evade the pursuit of the Xeno-Leviathan and discover what awaits at the far edge of the Dead Zone.
MODのリリースに先駆けて公開された公式トレーラー（動画リンク）のサムネイルには、ストーリーに登場する4つの施設を示すものと思われるシンボルが確認できる。そのうち、防衛技術研究施設に対応すると考えられる赤いシンボルは、現在ゲーム内で使用されているデザインとは異なり、「The Red Plague」に登場するシンボルと同一の意匠となっている。
シンボル変更の経緯については不明である。旧デザインを「The Red Plague」側で流用した可能性、あるいは両大型MODの関連性を示唆する意図的な演出である可能性などが考えられるが、いずれも推測の域を出ない。
なお、本MODのエンドクレジットには「The Red Plague integration」という役職名が確認できる。少なくとも制作段階において、両MOD間で何らかの情報共有や協力体制が存在していた可能性は高い。
他の大型MODとの互換性については、一部注意が必要なものの、共存自体は可能である。
『Return of the Ancients』との同時インストールは可能だが、デッドゾーンに出現する成体ガルガンチュアリヴァイアサンの影響により、本MOD終盤のデッドゾーン内イベントの進行が著しく困難になるため注意が必要である。また、成体ガルガンチュアリヴァイアサンとプロトタイプが干渉することで、予測不能な挙動やゲームのクラッシュが発生する可能性も報告されている。
『The Red Plague』との共存も可能である。ただし、同MODのストーリーを進行させるとデッドゾーンへの進入が不可能になるため、本MODのストーリー進行も不可能となる。
そのため、本MODのストーリー攻略を目的とする場合、これらの大型MODとの同時導入は推奨されない。一方で、『The Red Plague』のように多数の新たな探索地点や危険な生物を追加するMODを攻略する際には、本MODで追加される各種装備やプロトタイプの機能が大いに役立つだろう。
The thumbnail of the official trailer released prior to the MOD’s launch (video link) contains symbols that appear to represent the four facilities featured in the story. Among them, the red symbol thought to correspond to the Defensive Technologies Research Facility differs from the design currently used in-game, and uses the same motif as a symbol appearing in “The Red Plague”.
The reason for this symbol change is unknown. It is possible that the old design was reused in “The Red Plague,” or that it was an intentional hint suggesting a connection between the two large-scale MODs, but either interpretation remains speculative.
In addition, the end credits of this MOD include the role title “The Red Plague integration.” This strongly suggests that, at least during production, some form of information sharing or collaboration existed between the two MODs.
Compatibility with other large-scale MODs requires some caution, although coexistence itself is possible.
Installing this MOD alongside Return of the Ancients is possible. However, the adult Gargantuan Leviathan that appears in the Dead Zone can make the late-game Dead Zone events in this MOD significantly more difficult to progress through. In addition, unpredictable behavior or game crashes may occur if the adult Gargantuan Leviathan and the Prototype interfere with each other.
Coexistence with The Red Plague is also possible. However, once the story of that MOD has progressed, entering the Dead Zone becomes impossible, which in turn prevents the story of this MOD from progressing.
For these reasons, installing these large-scale MODs at the same time is not recommended if the goal is to complete this MOD’s story. On the other hand, when playing through MODs such as The Red Plague, which add many new exploration sites and dangerous creatures, the equipment and Prototype functions added by this MOD can be extremely useful.
As of July 2026, this is the first so-called “large-scale MOD” for Subnautica to reach completion among MODs that add a substantial amount of new story content, creatures, facilities, and other features.
The MOD was first released in August 2025. About one year later, in June 2026, the major “Phase Gate Update” was released, adding a large amount of new content and bringing the MOD’s story to its conclusion.
On August 23, 2026, the development team behind this mod, Prototech, transitioned into a newly established indie game studio called Aryx Games.
Development of The Prototype Expansion has officially come to an end, and the team announced on its official Discord server that it will now focus primarily on developing its original game, Tundra (working title).
Although relatively little information about Tundra has been revealed so far, players will take control of a canine robot and explore a cold, unforgiving planet overrun by machinery that is gradually harvesting the world from its surface all the way down to its core. The game has officially been described as “an open-world take on a cave-diving Metroidvania,” although the developers have noted that it may not necessarily meet every conventional criterion of the Metroidvania genre.
The official Discord server has been renamed from Prototech to Aryx Games, but discussion of this mod, including questions and bug reports, is still welcome. Aryx Games is also currently recruiting programmers, artists, and other contributors to help with the development of Tundra.
