v3.25.3

Document and Entity Information	Nov. 06, 2025
Cover [Abstract]
Amendment Flag	false
Entity Central Index Key	0001650648
Document Type	8-K
Document Period End Date	Nov. 06, 2025
Entity Registrant Name	4D Molecular Therapeutics, Inc.
Entity Incorporation State Country Code	DE
Entity File Number	001-39782
Entity Tax Identification Number	47-3506994
Entity Address, Address Line One	5858 Horton Street
Entity Address, Address Line Two	#455
Entity Address, City or Town	Emeryville
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94608
City Area Code	(510)
Local Phone Number	505-2680
Written Communications	false
Soliciting Material	false
Pre Commencement Tender Offer	false
Pre Commencement Issuer Tender Offer	false
Security 12b Title	Common Stock, $0.0001 par value per share
Trading Symbol	FDMT
Security Exchange Name	NASDAQ
Entity Emerging Growth Company	false

Boolean flag that is true when the XBRL content amends previously-filed or accepted submission.

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No definition available.

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- Definition

Area code of city

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- Definition

Cover page.

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- Definition

For the EDGAR submission types of Form 8-K: the date of the report, the date of the earliest event reported; for the EDGAR submission types of Form N-1A: the filing date; for all other submission types: the end of the reporting or transition period. The format of the date is YYYY-MM-DD.

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No definition available.

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The type of document being provided (such as 10-K, 10-Q, 485BPOS, etc). The document type is limited to the same value as the supporting SEC submission type, or the word 'Other'.

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No definition available.

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- Definition

Address Line 1 such as Attn, Building Name, Street Name

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No definition available.

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- Definition

Address Line 2 such as Street or Suite number

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No definition available.

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Name of the City or Town

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No definition available.

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Code for the postal or zip code

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No definition available.

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Name of the state or province.

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No definition available.

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- Definition

A unique 10-digit SEC-issued value to identify entities that have filed disclosures with the SEC. It is commonly abbreviated as CIK.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Exchange Act
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- Definition

Indicate if registrant meets the emerging growth company criteria.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Commission file number. The field allows up to 17 characters. The prefix may contain 1-3 digits, the sequence number may contain 1-8 digits, the optional suffix may contain 1-4 characters, and the fields are separated with a hyphen.

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No definition available.

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Two-character EDGAR code representing the state or country of incorporation.

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No definition available.

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The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Exchange Act
-Number 240
-Section 12
-Subsection b-2

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- Definition

The Tax Identification Number (TIN), also known as an Employer Identification Number (EIN), is a unique 9-digit value assigned by the IRS.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Exchange Act
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-Section 12
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- Definition

Local phone number for entity.

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No definition available.

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- Definition

Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Exchange Act
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Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Title of a 12(b) registered security.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Name of the Exchange on which a security is registered.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Exchange Act
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Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as soliciting material pursuant to Rule 14a-12 under the Exchange Act.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Exchange Act
-Number 240
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-Subsection 12

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Trading symbol of an instrument as listed on an exchange.

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No definition available.

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- Definition

Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as written communications pursuant to Rule 425 under the Securities Act.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Securities Act
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-Section 425

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4D Molecular Therapeutics, Inc. 8-K