Inclusion Criteria:

        Phase 2 part: Patients with confirmed diagnosis of MF who meet all of the following
        criteria:

          -  ANC ≥ 1 x 10^9/L without the assistance of granulocyte growth factors

          -  Peripheral blood blast count <10%

          -  ECOG performance status ≤ 2.

          -  Adequate hematological, renal, hepatic, and coagulation laboratory assessments

          -  No prior treatment with a BET inhibitor

          -  Patients must give written informed consent to participate in this study before the
             performance of any study-related procedure.

        For Arm 1 and 2 the following criteria should be considered:

          -  Patients with confirmed diagnosis of MF who meet all of the following criteria

          -  Dynamic International Prognostic Scoring System (DIPSS) risk category of
             intermediate-2 or higher

          -  Spleen volume ≥ 450 cm^3 by MRI or CT for Cohorts 1B and 2B OR RBC transfusion
             dependent (defined as an average of ≥2 units of RBC transfusions per month over the 12
             weeks prior to enrollment for Cohorts 1A and 2A)

          -  At least 2 symptoms measurable (Score ≥ 1) using the Myelofibrosis Symptom Assessment
             Form Version 4.0 (MFSAF v4.0)

          -  Platelet count ≥ 75 x 10^9/L without the assistance of thrombopoietic factors or
             transfusions for at least 14 days

        Monotherapy Arm (Arm 1): Previously treated with a JAK inhibitor and be intolerant,
        resistant, refractory, or lost response to the JAK inhibitor; have not received the JAK
        inhibitor within 2 weeks prior to the start of study drug, or are ineligible to be treated
        with a JAK inhibitor

        Combination Arm (Arm 2): Must have received single agent ruxolitinib and be on a stable
        dose for a minimum 8 weeks but have disease that is not being adequately controlled by
        ruxolitinib

        For Arm 3 (JAK inhibitors naïve) the following criteria should be considered:

          -  Patients with confirmed diagnosis of MF who meet all of the following criteria

          -  Dynamic International Prognostic Scoring System (DIPSS) risk category of
             intermediate-2 or higher

          -  Platelet count ≥ 100 x 10^9/L without the assistance of thrombopoietic factors or
             transfusions

          -  Spleen volume ≥ 450 cm^3 by MRI/CT

          -  At least 2 symptoms measurable (Score ≥ 3) or a total score of ≥ 10 using the MFSAF
             v4.0

          -  No prior treatment with JAKi allowed

        For Arm 4 (ET Expansion) the following criteria should be considered:

          -  Patients with a confirmed diagnosis of ET

          -  High-risk disease, defined as meeting at least one of the following criteria:

          -  Age > 60 years

          -  Platelet count > 1500 × 10^9/L (at any point during the patient's disease)

          -  Previously documented thrombosis, erythromelalgia, or migraine

          -  Previous hemorrhage related to ET

          -  Diabetes or hypertension requiring pharmacological therapy for > 6 months

          -  Have ≥2 symptoms with an average score ≥ 3 over the 7-day period prior to Cycle 1 Day
             1 or an average total score of ≥15 over the 7-day period prior to Cycle 1 Day 1 using
             the using the MPN SAF

               -  Platelets > 600 × 10^9/L

               -  Resistant or intolerant to HU

        Exclusion Criteria:

          -  Current known active or chronic infection with human immunodeficiency virus (HIV),
             Hepatitis B or Hepatitis C.

          -  Impaired cardiac function or clinically significant cardiac diseases

          -  Patients with Child-Pugh Class B or C

          -  Impairment of gastrointestinal (GI) function or GI disease that could significantly
             alter the absorption of CPI-0610 and/or ruxolitinib, including any unresolved nausea,
             vomiting, or diarrhea that is CTCAE Grade >1

          -  Prior treatment with a BET inhibitor.

          -  Pregnant or lactating women

          -  Any other concurrent severe and/or uncontrolled concomitant medical condition that
             could compromise participation in the study

          -  Patients unwilling or unable to comply with this study protocol.