Norges Bank reports 7.73% stake in Upstream Bio

Rhea-AI Filing Summary

Norges Bank, the central bank of Norway and an investment adviser, reports its beneficial ownership of common stock of Upstream Bio, Inc. on an amended Schedule 13G. Norges Bank reports beneficial ownership of 4,206,586 shares of common stock, representing 7.7299% of the class.

Of this position, Norges Bank has 3,768,619 shares with sole power to vote and 3,768,619 shares with sole power to dispose. It reports 437,967 shares with shared power to dispose and no shared voting power. Certain shares are reported as invested on behalf of the Government of Norway, and Norges Bank certifies that its foreign regulatory scheme is substantially comparable to that of functionally equivalent U.S. institutions.

Key Figures

Beneficially owned shares: 4,206,586 shares Ownership percentage: 7.7299% Sole voting power: 3,768,619 shares +3 more

6 metrics

Beneficially owned shares 4,206,586 shares Common stock of Upstream Bio, Inc. reported by Norges Bank

Ownership percentage 7.7299% Percent of Upstream Bio common stock class held by Norges Bank

Sole voting power 3,768,619 shares Shares for which Norges Bank has sole power to vote

Sole dispositive power 3,768,619 shares Shares for which Norges Bank has sole power to dispose

Shared dispositive power 437,967 shares Shares for which Norges Bank has shared power to dispose

Signature date 08/12/2026 Date the certification was signed by Business and Regulatory Compliance

Key Terms

beneficially owned, Sole Voting Power, Sole Dispositive Power, Shared Dispositive Power, +2 more

6 terms

beneficially owned financial

"Ownership (a) | Amount beneficially owned: 4206586"

Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.

Sole Voting Power financial

"5 | Sole Voting Power 3,768,619.00"

Sole voting power is the exclusive right to cast votes attached to a shareholder’s stock without needing approval from anyone else. Like holding the only remote control for a TV, it lets that holder decide corporate matters such as board members, mergers, and policy changes, making it important to investors because it concentrates control and can strongly influence a company’s strategy and the value of its shares.

Sole Dispositive Power financial

"7 | Sole Dispositive Power 3,768,619.00"

Sole dispositive power is the exclusive legal authority to decide what happens to a security — for example, whether to sell, transfer, or retain shares — without needing anyone else’s permission. Investors care because it signals who truly controls the economic outcome of an investment: like holding the only key to a safe, the holder can realize gains or losses and may trigger regulatory reporting, insider rules, or influence over corporate ownership.

Shared Dispositive Power financial

"8 | Shared Dispositive Power 437,967.00"

Schedule 13D regulatory

"otherwise be disclosed in a Schedule 13D."

A Schedule 13D is a legal document that investors file with regulators when they buy a large enough stake in a company to potentially influence its management or decisions. It provides details about the investor’s intention, ownership stake, and plans, helping other investors understand who is gaining control and what their motives might be.

Investment Adviser financial

"12 FI, | Investment Adviser"

An investment adviser is a person or firm that professionally manages money and gives recommendations about buying, selling, or holding investments. Like a financial coach or guide, they have a legal duty to act in a client's best financial interest, so their advice, fees and potential conflicts can directly affect returns and risk — making their role important for investors who want informed, accountable help with portfolios.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

How many Upstream Bio (UPB) shares does Norges Bank report owning?

Norges Bank reports beneficial ownership of 4,206,586 shares of Upstream Bio common stock. This position represents a 7.7299% stake in the company’s outstanding common shares as disclosed in the Schedule 13G/A filing.

What percentage of Upstream Bio (UPB) does Norges Bank hold according to this filing?

Norges Bank reports holding 7.7299% of Upstream Bio’s common stock. This percentage is based on 4,206,586 beneficially owned shares as detailed in the ownership section of the Schedule 13G/A amendment.

How much voting power does Norges Bank have in Upstream Bio (UPB)?

Norges Bank reports 3,768,619 shares with sole voting power and 0 shares with shared voting power in Upstream Bio. This sole voting authority applies to the same number of shares over which it has sole dispositive power.

What dispositive powers over Upstream Bio (UPB) shares does Norges Bank report?

Norges Bank has sole dispositive power over 3,768,619 shares and shared dispositive power over 437,967 shares of Upstream Bio. In total, these interests comprise the 4,206,586 beneficially owned shares reported in the filing.

Who is the filing person and what is their role regarding Upstream Bio (UPB)?

The filing person is Norges Bank, the central bank of Norway acting as an investment adviser. It files a Schedule 13G/A reporting its beneficial ownership and management of Upstream Bio common stock, including certain shares invested on behalf of the Government of Norway.

When was this Upstream Bio (UPB) Schedule 13G/A certification signed and by whom?

The certification was signed on 08/12/2026 by Stanislav Boiadjiev, Business and Regulatory Compliance. The signer certifies the comparability of Norges Bank’s foreign regulatory scheme and undertakes to furnish additional information otherwise disclosed in a Schedule 13D upon request.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 08/12/2026 - 06:37 AM Accepted by SEC EDGAR 08/12/2026 - 06:36 AM Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 1)

Upstream Bio, Inc.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

91678A107

(CUSIP Number)

06/30/2026

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

schemaVersion:

SCHEDULE 13G

CUSIP Number(s): 91678A107

1

Names of Reporting Persons

Norges Bank

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

NORWAY

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 3,768,619.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 3,768,619.00
8	Shared Dispositive Power 437,967.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

4,206,586.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

7.7299 %

12

Type of Reporting Person (See Instructions)

FI, OO

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Upstream Bio, Inc.
(b)	Address of issuer's principal executive offices: 890 Winter Street, Suite 200, Waltham, MA, 02451
Item 2.
(a)	Name of person filing: Norges Bank
(b)	Address or principal business office or, if none, residence: Bankplassen 2, PO Box 1179 Sentrum, Oslo, NO-0107, Oslo, Norway
(c)	Citizenship: Norway
(d)	Title of class of securities: Common Stock
(e)	CUSIP No.: 91678A107
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
	Investment Adviser
Item 4.	Ownership
(a)	Amount beneficially owned: 4206586
(b)	Percent of class: 7.7299 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 3768619
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: 3768619
	(iv) Shared power to dispose or to direct the disposition of: 437967
Item 5.	Ownership of 5 Percent or Less of a Class.
	Not Applicable
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required. Certain shares reported herein are invested on behalf of the Government of Norway.
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11. I also certify that, to the best of my knowledge and belief, the foreign regulatory scheme applicable to the investment management division of Norges Bank, the central bank of Norway, is substantially comparable to the regulatory scheme applicable to the functionally equivalent U.S. institution(s). I undertake to furnish to the Commission staff, upon request, information that would otherwise be disclosed in a Schedule 13D.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Norges Bank

Signature:	Stanislav Boiadjiev
Name/Title:	Business and Regulatory Compliance
Date:	08/12/2026