• Adult patients with previously untreated CLL defined following IWCLL criteria (Hallek, 2018).

• Must understand and voluntarily sign an informed consent form.

• Age ≥ 18 years at the time of signing the informed consent form and must be able to adhere to the study visit schedule and other protocol requirements.

• Must have a documented diagnosis of CLL or SLL \[IWCLL guidelines for diagnosis and treatment of CLL (Hallek, 2018)\] meeting at least one of the following criteria:

‣ Evidence of progressive marrow failure as manifested by the development of, or worsening of, anemia and/or thrombocytopenia.

⁃ Massive (i.e. ≥6 cm below the left costal margin) or progressive or symptomatic splenomegaly.

⁃ Massive nodes (i.e. ≥10 cm in longest diameter) or progressive or symptomatic lymphadenopathy.

⁃ Progressive lymphocytosis with an increase of ≥50% over a 2-month period, or lymphocyte doubling time (LDT) of less than 6 months.

⁃ A minimum of any one of the following disease-related symptoms: unintentional weight loss ≥ 10% within the previous 6 months, significant fatigue (i.e., ECOG PS 2 or worse; cannot work or unable to perform usual activities), fevers of greater than 38.0°C for 2 or more weeks without other evidence of infection, or night sweats for more than 1 month without evidence of infection.

⁃ Autoimmune complications including anemia or thrombocytopenia poorly responsive to corticosteroids.

⁃ Symptomatic or functional extranodal involvement (eg, skin, kidney, lung, spine).

• Must have an Eastern Cooperative Oncology Group (ECOG) performance status score of ≤2.

• Female patients of childbearing potential must practice highly effective methods of contraception initiated prior to first dose of study drug, for the duration of the study, and for ≥ 90 days after the last dose of zanubrutinib and 18 months after last dose of obinutuzumab.

• Male patients are eligible if vasectomized or if they agree to the use of barrier contraception with other applicable highly effective methods described below during the study treatment period and for ≥ 90 days after the last dose of zanubrutinib and 18 months after last dose of obinutuzumab.

• A woman is considered of childbearing potential, ie, fertile, following menarche and until becoming postmenopausal unless permanently sterile. Permanent sterilization methods include hysterectomy, bilateral salpingectomy, and bilateral oophorectomy. Contraception methods include the following:

⁃ Combined (estrogen- and progestogen- containing) hormonal contraception associated with the inhibition of ovulation - Oral, intravaginal, or transdermal.

⁃ Progestogen-only hormonal contraception associated with the inhibition of ovulation - Oral, injectable, implantable.

⁃ An intrauterine device.

⁃ Intrauterine hormone-releasing system.

⁃ Bilateral tubal occlusion.

⁃ Vasectomized partner (provided that the vasectomized partner is the sole sexual partner of the woman of childbearing potential study participant and that the vasectomized partner has received medical assessment of surgical success).

⁃ Sexual abstinence (defined as refraining from heterosexual intercourse during the entire period of risk associated with the study treatment, starting the day prior to first dose of study drug, for the duration of the study, and for ≥ 90 days after the last dose of zanubrutinib or ibrutinib. Total sexual abstinence should only be used as a contraceptive method if it is in line with the patients' usual and preferred lifestyle. Periodic abstinence (eg, calendar, ovulation, symptothermal, post-ovulation methods), declaration of abstinence for the duration of exposure to investigational medicinal product, and withdrawal are not acceptable methods of contraception.

• Of note, barrier contraception (including male and female condoms with or without spermicide) is not considered a highly effective method of contraception, and, if used, this method must be used in combination with another acceptable method listed above.

• If patient is using hormonal contraceptives such as birth control pills or devices, a barrier method of contraception (eg, condoms) must also be used.

• A postmenopausal state is defined as no menses for 12 months without an alternative medical cause. A high follicle-stimulating hormone level in the postmenopausal range may be used to confirm a postmenopausal state in women not using hormonal contraception or hormonal replacement therapy. However, in the absence of 12 months of amenorrhea, a single follicle-stimulating hormone measurement is insufficient.

• Female subjects of childbearing potential must have a negative pregnancy test at screening. Females of child bearing potential are defined as sexually mature women without prior hysterectomy or who have had any evidence of menses in the past 12 months. However, women who have been amenorrheic for 12 or more months are still considered to be of childbearing potential if the amenorrhea is possibly due to other causes, including prior chemotherapy, anti-estrogens, or ovarian suppression.