Restrict width in ConstraintLayout by another view

yes you can by using match_constraint (0dp) which equal to match_parent for other layout, so by using match_constraint we set weight for first view which will occupies all available space also add

app:layout_constraintWidth_default="wrap"

to apply default width behavior as wrap_content

here is code with change

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto">

        <TextView
            android:id="@+id/value"
            android:layout_width="0dp"
            app:layout_constraintWidth_default="wrap"
            android:layout_height="wrap_content"
            android:layout_marginStart="8dp"
            android:lines="1"
            app:layout_constraintBaseline_toBaselineOf="@+id/unit"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintHorizontal_chainStyle="packed"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toLeftOf="@id/unit"
            tools:text="12533939532" />

        <TextView
            android:id="@+id/unit"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginEnd="8dp"
            android:layout_marginStart="8dp"
            app:layout_constraintLeft_toRightOf="@id/value"
            app:layout_constraintRight_toRightOf="parent"
            tools:text="km" />

    </android.support.constraint.ConstraintLayout>

got some explanation from site

Better view dimension controls

The new available behaviors when a dimension is set to 0dp (MATCH_CONSTRAINT). As before, both endpoints (left/right or top/bottom) need to be connected to targets.

layout_constraintWidth_default = spread (default, similar to the previous behavior)
layout_constraintWidth_default = wrap
layout_constraintHeight_default = spread
layout_constraintHeight_default = wrap

Wrap provides a significant new behaviour, with the widget resizing as if wrap_content was used, but limited by the connected constraints. A widget will thus not grow beyond the endpoints.

http://tools.android.com/recent/constraintlayoutbeta5isnowavailable