Alumis and ACELYRIN Reaffirm Strategic and Financial Rationale of Proposed Merger Combined company to benefit from differentiated late-stage portfolio of therapies and strong balance sheet SOUTH SAN FRANCISCO, Calif. and

Alumis and ACELYRIN Reaffirm Strategic and

Financial Rationale of Proposed Merger

Combined company to benefit from differentiated

late-stage portfolio of therapies and strong balance sheet

SOUTH SAN FRANCISCO, Calif. and LOS ANGELES, March 4, 2025

- Alumis Inc. (Nasdaq: ALMS) ("Alumis") and ACELYRIN, INC. (Nasdaq: SLRN) ("ACELYRIN") today reaffirmed

their commitment to merge in an all-stock transaction, which will create a leading clinical stage biopharma company in immune-mediated

Martin Babler, President, Chief Executive Officer and Chairman of Alumis,

said, "Alumis and ACELYRIN together will advance exciting breakthroughs for patients and drive long-term value for stockholders

through the creation of a leading clinical stage biopharma company in immune-mediated diseases. The combined company will have a significantly

strengthened financial position to support a highly differentiated and diverse pipeline with multiple catalysts. With our management team's

successful track-record of developing innovative therapies and an extended runway afforded by combining with ACELYRIN, the transaction

will allow us to unlock the value of the combined portfolio for current and future investors and address what we believe is a current

dislocation with our valuation. We look forward to completing the combination next quarter and delivering the meaningful benefits of the

merger for both companies' stakeholders."

"The ACELYRIN Board of Directors is confident that the all-stock

transaction with Alumis maximizes long-term value for ACELYRIN stockholders and continues to recommend that stockholders support the planned

merger," said Mina Kim, Chief Executive Officer of ACELYRIN. "We chose to enter into the merger agreement with Alumis after

a comprehensive assessment of strategic alternatives, and believe this is the best outcome for ACELYRIN stockholders. We're

excited about the combined company's potential for significant value creation as a result of its expanded portfolio, strong financial

foundation and proven leadership."

The combined company is expected to benefit from:

The transaction is expected to close in the second quarter of 2025,

subject to approval by the stockholders of both companies and satisfaction of other customary closing conditions. Alumis expects to publicly

file the S-4 and begin mailing of the proxy statement related to the transaction promptly following completion of the fiscal year 2024

audits and filing of Annual Reports on Form 10-K by each of Alumis and ACELYRIN.

Alumis and ACELYRIN will file an investor presentation with the Securities

and Exchange Commission with background information regarding ACELYRIN's strategic review process, which will be available this

Morgan Stanley & Co. LLC is serving as financial advisor to

Alumis, and Cooley LLP is serving as its legal counsel. Guggenheim Securities, LLC is serving as financial advisor to ACELYRIN and Fenwick &

West LLP and Paul Hastings LLP are serving as its legal counsel.

Alumis is a clinical-stage biopharmaceutical company developing oral

therapies using a precision approach to optimize clinical outcomes and significantly improve the lives of patients with immune-mediated

diseases. Leveraging its proprietary precision data analytics platform, Alumis is building a pipeline of molecules with the potential

to address a broad range of immune-mediated diseases as monotherapy or combination therapies. Alumis' most advanced product candidate,

ESK-001, is an oral, highly selective, small molecule, allosteric inhibitor of TYK2 that is currently being evaluated for the treatment

of patients with moderate-to-severe plaque psoriasis and systemic lupus erythematosus. Alumis is also developing A-005, a CNS-penetrant,

allosteric TYK2 inhibitor for the treatment of neuroinflammatory and neurodegenerative diseases. Beyond TYK2, Alumis' proprietary

precision data analytics platform and drug discovery expertise have led to the identification of additional preclinical programs that

exemplify its precision approach. Incubated by Foresite Labs and led by a team of industry veterans experienced in small-molecule compound

drug development for immune-mediated diseases, Alumis is pioneering a precision approach to drug development to potentially produce the

next generation of treatment to address immune dysfunction. For more information, visit www.alumis.com.

ACELYRIN is focused on providing patients life-changing new treatment

options by identifying, acquiring, and accelerating the development and commercialization of transformative medicines. ACELYRIN's

lead program, lonigutamab, is a subcutaneously delivered monoclonal antibody targeting IGF-1R being investigated for the treatment of

thyroid eye disease.

Financial Disclaimer

Alumis' and ACELYRIN's audited consolidated financial statements

for the year ended December 31, 2024 are not yet available. Accordingly, the information presented herein regarding cash, cash equivalents

and marketable securities as of December 31, 2024, reflects each of Alumis' and ACELYRIN's preliminary financial data,

subject to the completion of Alumis' and ACELYRIN's financial closing procedures and any adjustments that may result from

the completion of the review and audit of Alumis' and ACELYRIN's consolidated financial statements for the year ended December 31,

2024, respectively. Actual financial results that will be reflected in each of Alumis' and ACELYRIN's Annual Reports on Form 10-K

for the year ended December 31, 2024, when they are completed and publicly disclosed may differ from the preliminary results presented

Forward-Looking Statements

This communication contains forward-looking statements within the meaning

of federal securities laws, including the "safe harbor" provisions of the Private Securities Litigation Reform Act of 1995.

Such statements are based upon current plans, estimates and expectations of management of Alumis and ACELYRIN in light of historical results

and trends, current conditions and potential future developments, and are subject to various risks and uncertainties that could cause

actual results to differ materially from such statements. The inclusion of forward-looking statements should not be regarded as a representation

that such plans, estimates and expectations will be achieved. Words such as "anticipate," "expect," "project,"

"intend," "believe," "may," "will," "should," "plan," "could,"

"continue," "target," "contemplate," "estimate," "forecast," "guidance,"

"predict," "possible," "potential," "pursue," "likely," and words and terms

of similar substance used in connection with any discussion of future plans, actions or events identify forward-looking statements. All

statements, other than statements of historical facts, including express or implied statements regarding the proposed transaction; the

conversion of equity interests contemplated by the agreement and plan of merger, dated as of February 6, 2025, by and among the parties

(the "merger agreement"); the issuance of common stock of Alumis contemplated by the merger agreement; the expected filing

by Alumis with the Securities and Exchange Commission (the "SEC") of a registration statement on Form S-4 (the "registration

statement") and a joint proxy statement/prospectus of Alumis and ACELYRIN to be included therein (the "joint proxy statement/prospectus");

the expected timing of the closing of the proposed transaction; the ability of the parties to complete the proposed transaction considering

the various closing conditions; the expected benefits of the proposed transaction; the sufficiency of the combined company's capital

resources; the combined company's cash runway; the competitive ability and position of the combined company; the clinical pipeline

of the combined company; and any assumptions underlying any of the foregoing, are forward-looking statements.

Risks and uncertainties include, among other things, (i) the risk

that the proposed transaction may not be completed in a timely basis or at all, which may adversely affect Alumis' and ACELYRIN's

businesses and the price of their respective securities; (ii) the potential failure to receive, on a timely basis or otherwise, the

required approvals of the proposed transaction, including stockholder approvals by both Alumis' stockholders and ACELYRIN'S

stockholders, and the potential failure to satisfy the other conditions to the consummation of the transaction; (iii) the effect

of the announcement, pendency or completion of the proposed transaction on each of Alumis' or ACELYRIN's ability to attract,

motivate, retain and hire key personnel and maintain relationships with partners, suppliers and others with whom Alumis or ACELYRIN does

business, or on Alumis' or ACELYRIN's operating results and business generally; (iv) that the proposed transaction may

divert management's attention from each of Alumis' and ACELYRIN's ongoing business operations; (v) the risk of

any legal proceedings related to the proposed transaction or otherwise, or the impact of the proposed transaction thereupon, including

resulting expense or delay; (vi) that Alumis or ACELYRIN may be adversely affected by other economic, business and/or competitive

factors; (vii) the occurrence of any event, change or other circumstance that could give rise to the termination of the merger agreement

, including in circumstances which would require Alumis or ACELYRIN to pay a termination fee; (viii) the risk that restrictions during

the pendency of the proposed transaction may impact Alumis' or ACELYRIN's ability to pursue certain business opportunities

or strategic transactions; (ix) the risk that the anticipated benefits and synergies of the proposed transaction may not be fully

realized or may take longer to realize than expected; (x) the impact of legislative, regulatory, economic, competitive and technological

changes; (xi) risks relating to the value of Alumis securities to be issued in the proposed transaction; (xii) the risk that

integration of the proposed transaction post-closing may not occur as anticipated or the combined company may not be able to achieve the

growth prospects expected from the transaction; (xiii) the effect of the announcement, pendency or completion of the proposed transaction

on the market price of the common stock of each of Alumis and ACELYRIN; (xiv) the implementation of each of Alumis' and ACELYRIN's

business model and strategic plans for product candidates and pipeline, and challenges inherent in developing, commercializing, manufacturing,

launching, marketing and selling potential existing and new products and product candidates; (xv) the scope, progress, results and

costs of developing Alumis' and ACELYRIN's product candidates and any future product candidates, including conducting preclinical

studies and clinical trials, and otherwise related to the research and development of Alumis' and ACELYRIN's pipeline; (xvi) the

timing and costs involved in obtaining and maintaining regulatory approval for Alumis' and ACELYRIN's current or future product

candidates, and any related restrictions, limitations and/or warnings in the label of any approved product; (xvii) the market for,