Inclusion Criteria:
* 1\. The participant voluntarily agrees to participate in this study, signs the informed consent form, and strictly adheres to the requirements of the study protocol.
* 2\. Age ≥18 years and ≤75 years at enrollment, regardless of gender.
* 3\. Histologically confirmed unresectable locally advanced or metastatic G/GEJ adenocarcinoma, with inclusion criteria specifying HER2- status (HER2+ status defined as IHC3+ or IHC2+ and FISH+).
* 4\. No prior systemic treatment for unresectable locally advanced or metastatic G/GEJ adenocarcinoma; previous neoadjuvant and/or adjuvant therapy is acceptable, but all systemic treatments must have been completed at least 12 months prior to the diagnosis of unresectable or metastatic disease.
* 5\. At least one measurable tumor lesion according to RECIST 1.1 criteria.
* 6\. ECOG PS of 0 or 1.
* 7\. Life expectancy ≥3 months.
* 8\. Fully recovered from any toxicities related to prior treatments prior to enrollment in the study.
* 9\. BMI \>18.
* 10\. Adequate function of major organs
* 11\. Fertile subjects must use appropriate contraception during the study and for 120 days after the end of the study. They must have a negative serum pregnancy test within 7 days prior to enrollment and must not be breastfeeding.
Exclusion Criteria:
* 1\. Any unstable systemic disease: including active infection, uncontrolled hypertension, unstable angina, angina that started within the last 3 months, congestive heart failure (New York Heart Association \[NYHA\] ≥Class II), myocardial infarction within 6 months prior to enrollment, severe arrhythmias requiring medication, or hepatic, renal, or metabolic diseases.
* 2\. Symptomatic brain and/or leptomeningeal metastases.
* 3\. Known deficiency of dihydropyrimidine dehydrogenase (DPD).
* 4\. QT/QTc interval \>450 ms for males, \>470 ms for females.
* 5\. History of other malignancies within 5 years prior to enrollment, with the exception of adequately treated cervical carcinoma in situ, basal cell carcinoma, or squamous cell carcinoma of the skin.
* 6\. History of organ transplantation or autologous/allogeneic stem cell transplantation.
* 7\. Currently receiving systemic immunotherapy or hormone therapy other than physiologic replacement therapy.
* 8\. Other concurrent anti-tumor treatments.
* 9\. Known hypersensitivity or allergic reaction to any component of the study treatment.
* 10\. Previous exposure to docetaxel or oxaliplatin (except for adjuvant chemotherapy).
* 11\. Previous exposure to immune checkpoint inhibitors (e.g., anti-PD-1 antibodies, anti-PD-L1 antibodies, anti-CTLA-4 antibodies), immune checkpoint agonists (e.g., antibodies targeting ICOS, CD40, CD137, GITR, OX40), or any immunotherapy targeting tumor immune mechanisms.
* 12\. Participants with severe bone marrow failure.
* 13\. Any disease, metabolic disorder, or physical examination or laboratory findings that suggest contraindications to the study drug or high-risk factors for treatment complications.
* 14\. Known or self-reported human immunodeficiency virus (HIV) infection.
* 15\. Participants who are HBV or HCV positive.
* 16\. Pregnant or breastfeeding.
* 17\. Received a live vaccine within 4 weeks prior to the first dose, or plans to receive a live vaccine during the study.
* 18\. Participated in any investigational drug treatment or used any investigational device within 4 weeks prior to the first dose.
* 19\. Any condition that the investigator believes may pose a risk to the participant receiving the study drug, or may interfere with the evaluation of the study drug, the safety of the participant, or the interpretation of the study results.
