With Base64:
In [3]: %time mlab.set_variable('ha', np.linspace(1.1, 2, 10000).reshape(100, 100))
CPU times: user 4.31 ms, sys: 1.61 ms, total: 5.92 ms
Wall time: 163 ms
Out[3]: {'success': 'true', 'result': 1, 'message': 'Successfully completed request'}

In [4]: %time b = mlab.get_variable('ha')
CPU times: user 3.93 ms, sys: 1.09 ms, total: 5.02 ms
Wall time: 66.8 ms

In [5]: b
Out[5]: b
array([[ 1.1       ,  1.10009001,  1.10018002, ...,  1.10873087,
         1.10882088,  1.10891089],
       [ 1.1090009 ,  1.10909091,  1.10918092, ...,  1.11773177,
         1.11782178,  1.11791179],
       [ 1.1180018 ,  1.11809181,  1.11818182, ...,  1.12673267,
         1.12682268,  1.12691269],
       ..., 
       [ 1.97308731,  1.97317732,  1.97326733, ...,  1.98181818,
         1.98190819,  1.9819982 ],
       [ 1.98208821,  1.98217822,  1.98226823, ...,  1.99081908,
         1.99090909,  1.9909991 ],
       [ 1.99108911,  1.99117912,  1.99126913, ...,  1.99981998,
         1.99990999,  2.        ]])

On master branch:
In [5]: %time mlab.set_variable('ha', np.linspace(1.1, 2, 10000).reshape(100, 100))
CPU times: user 16.7 ms, sys: 1.08 ms, total: 17.7 ms
Wall time: 1.19 s
Out[5]: {'result': 1, 'message': 'Successfully completed request', 'success': 'true'}

In [6]: %time b = mlab.get_variable('ha')
CPU times: user 5.33 ms, sys: 1.2 ms, total: 6.54 ms
Wall time: 821 ms

In [7]: type(b)
Out[7]: list