Elon Musk and musician Grimes have three publicly identified children together: X Æ A-Xii, Exa Dark Sideræl, and Techno Mechanicus. Their births and names entered the public record at different times, and much of the children’s current private life remains undisclosed.
At a glance
| Child | Publicly reported name | Nickname | What is publicly known about the disclosure |
|---|---|---|---|
| Oldest | X Æ A-Xii | X, or Lil X | Born in 2020; Elon Musk announced the original spelling, X Æ A-12, shortly after the birth. |
| Middle child | Exa Dark Sideræl | Y | Born via surrogate in December 2021; Grimes disclosed her name in a Vanity Fair profile published in March 2022. |
| Youngest | Techno Mechanicus | Tau | Reportedly born in June 2022; the child’s existence and name became public through reporting connected to Walter Isaacson’s 2023 biography of Musk. |
Elon Musk and musician Grimes—whose legal name is Claire Boucher—have three publicly identified children together: X Æ A-Xii, Exa Dark Sideræl, and Techno Mechanicus. The first child’s unusual name became public immediately, the second child was disclosed by Grimes several months after her birth, and the third was kept private until 2023 reporting.
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That chronology matters. The public record explains how the names entered the news and, in some cases, what the parents said inspired them. It does not provide a complete or authoritative account of the children’s current homes, custody schedule, schooling, medical information, or day-to-day lives.
X Æ A-Xii: Musk and Grimes’ first child
From “X Æ A-12” to “X Æ A-Xii”
On May 5, 2020, Musk posted that the couple had named their newborn son “X Æ A-12 Musk.” The spelling later appeared in reporting as X Æ A-Xii, replacing the Arabic numerals “12” with the Roman-numeral form “Xii.” Contemporary coverage connected the change with California’s restrictions on characters permitted in official names and quoted Grimes as saying the Roman numerals looked better. See the reported account of the spelling change for that chronology.
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The child is commonly called X or Lil X. Because the parents have described parts of the name and its pronunciation differently at different times, there is no need to present one definitive spoken version as settled fact. Public renderings have included “X-Ash-A-Twelve” and “X A.I. Archangel.” The most precise short form is simply: X Æ A-Xii, commonly called X.
What the name is said to mean
Grimes explained the elements of the original name in symbolic and technological terms:
- X was associated with the unknown variable.
- Æ was described by Grimes as an elven spelling connected with AI, although Musk has described the sound or meaning differently.
- A-12 referred to the Lockheed A-12 reconnaissance aircraft, which Grimes associated with speed and nonviolence. She also linked the “A” with “Archangel.”
These are the parents’ publicly attributed inspirations, not an official translation of the name. The disagreement over pronunciation is one reason cautious wording is preferable to claiming that the name has one universally established reading. The Guardian’s contemporaneous explainer summarizes the original announcement and Grimes’s explanation.
Exa Dark Sideræl: their daughter known as Y
Birth and public disclosure
Grimes revealed in a Vanity Fair cover profile published on March 10, 2022, that she and Musk had welcomed a daughter via surrogate in December 2021. The child was identified as Exa Dark Sideræl and was sometimes called Y.
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The birth had not been publicly announced at the time it occurred. That distinction is important: Y is a reported nickname, not a publicly confirmed legal middle name, and the available reporting does not justify treating it as anything more than the name the parents sometimes used. The original Vanity Fair profile is the key source for the disclosure and the meanings Grimes attributed to the name.
The meanings Grimes attributed to Exa Dark Sideræl
According to Grimes:
- Exa refers to exaFLOPS, a measure used in supercomputing. “Exa” denotes a scale of one quintillion floating-point operations per second.
- Dark was connected with the unknown and the absence of photons. Grimes also associated it with the mystery of dark matter.
- Sideræl is pronounced by Grimes approximately “sigh-deer-ee-el.” She described it as an elven spelling of sidereal, a term related to deep-space or stellar time rather than ordinary Earth-relative time. She also connected the spelling with Galadriel from The Lord of the Rings.
As with X’s name, these explanations should be attributed to Grimes. They describe the inspirations she publicly gave for the name; they are not independently verified etymological definitions.
Techno Mechanicus: the child known as Tau
How the name became public
The couple did not announce the birth of their third child. Reporting in September 2023, around the publication of Walter Isaacson’s biography Elon Musk, identified the child as Techno Mechanicus and reported the nickname Tau. The same reports said the child was born in June 2022, but because the parents kept the birth private and the timing comes through secondary reporting, it is more accurate to say the child was reported to have been born in June 2022 rather than to supply an unsupported exact date.
The disclosure was tied to Walter Isaacson’s Elon Musk biography and coverage surrounding it. The book is relevant to the chronology because reporting about the biography brought the third child’s identity and name into the public record. It should not, however, be treated as an official family statement or as proof that every detail in secondary coverage has been independently confirmed.
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No reliable public explanation from Musk or Grimes establishes the meaning of the full name. It may be tempting to construct an interpretation from the words “techno” and “mechanicus,” but doing so would be speculation. The defensible facts are the reported name Techno Mechanicus and the reported nickname Tau. Tau should not automatically be expanded into a claimed legal name or a confirmed explanation of the naming choice.
Why the children’s privacy is part of the story
The three children have entered the public record in very different ways. Musk publicly posted X’s original name; Grimes chose to disclose Exa’s birth and name in an interview; and Techno’s existence surfaced later through reporting. That does not make the children’s private lives open-source material.
Recent coverage has described Grimes objecting to the children’s public exposure and expressing concern about their lives becoming public. Other reporting has discussed Musk bringing X to high-profile public events. Those public disagreements can be reported when relevant, but they do not establish the children’s private wishes or provide a reliable picture of their everyday lives. The Guardian’s reporting on public exposure and privacy concerns provides context without resolving every underlying family matter.
There is also no authoritative public source establishing a complete, current custody arrangement. Public reports have described parental-rights and privacy disputes, but readers should be wary of claims about where the children live, which parent has them at a particular time, what schools they attend, or how parenting responsibilities are divided. Court proceedings, agreements, or other relevant records may be private or sealed, and the children are minors.
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Musk and Grimes’ relationship timeline
- 2018: Musk and Grimes began dating.
- 2020: Their first child, X, was born, and the original form of his name was announced publicly.
- December 2021: Their daughter Exa was reported to have been born via surrogate.
- March 2022: Grimes’s Vanity Fair profile disclosed Exa’s birth and name. Around this period, public descriptions of the couple’s relationship characterized it as complicated or fluid, and Grimes announced a breakup.
- June 2022: Techno was reported to have been born, although the birth was not announced at the time.
- September 2023: Reporting connected to Isaacson’s biography identified Techno and the nickname Tau.
The relationship timeline supplies disclosure context, but it should not be used to reduce the children’s identities to their parents’ relationship status. Nor should these three children be conflated with Musk’s other children from other relationships.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What is—and is not—confirmed publicly
| Publicly documented | Not reliably established by the available record |
|---|---|
| The three reported names and public nicknames | A complete current custody schedule |
| The 2020 announcement and later spelling of X’s name | Current residences or school arrangements |
| Grimes’s stated inspirations for X’s and Exa’s names | Medical information or day-to-day parenting details |
| Exa’s reported December 2021 birth via surrogate | Techno’s exact birth date |
| Reporting that Techno was born in June 2022 and is nicknamed Tau | An official explanation for “Techno Mechanicus” or “Tau” |
In short, the names and disclosure history can be documented. A detailed narrative about the children’s current private circumstances cannot be responsibly assembled from the public sources reviewed here.
Frequently Asked Questions
How many children do Elon Musk and Grimes have together?
Elon Musk and Grimes have three publicly identified children: X Æ A-Xii, Exa Dark Sideræl and Techno Mechanicus.
What are Musk and Grimes’ children’s nicknames?
X Æ A-Xii is commonly called X or Lil X. Exa Dark Sideræl is sometimes called Y, while Techno Mechanicus is reported to be nicknamed Tau.
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Why was X Æ A-12 changed to X Æ A-Xii?
The name was initially announced as X Æ A-12 in May 2020 and later reported as X Æ A-Xii. Coverage connected the change from “12” to “Xii” with California naming restrictions and Grimes’s preference for the Roman-numeral styling.
What does Exa Dark Sideræl mean?
Grimes said Exa referred to exaFLOPS, Dark to the unknown or absence of photons, and Sideræl to a deep-space or sidereal concept. These are her publicly attributed inspirations, not independently verified definitions.
What is known about Techno Mechanicus?
Techno Mechanicus’s existence and name became public through 2023 reporting connected to Walter Isaacson’s biography of Musk. The child was reported to have been born in June 2022, but no reliable public explanation of the full name has been established.
The Bottom Line
Bottom line: Elon Musk and Grimes have three publicly identified children: X Æ A-Xii, commonly called X; Exa Dark Sideræl, sometimes called Y; and Techno Mechanicus, nicknamed Tau. X’s name was announced in 2020 and later changed in form, Grimes explained the inspirations attributed to Exa’s name in 2022, and Techno’s existence became public through reporting around Walter Isaacson’s 2023 biography. Beyond those facts, the children’s current custody, homes, schooling, and daily lives remain private and should not be presented as established public information.
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