Am using sentence windowing technique to fix the length of a sentence that my model sees. So, variable  length input shouldn’t be an issue
example:

input sentence = (‘EU’, ‘rejects’, ‘German’, ‘call’, ‘to’, ‘boycott’, ‘British’, ‘lamb’, ‘.’)
output_windows =
(’’, ‘’, ‘’, ‘EU’, ‘rejects’, ‘German’, ‘call’, ‘to’, ‘boycott’),
(’’, ‘’, ‘EU’, ‘rejects’, ‘German’, ‘call’, ‘to’, ‘boycott’, ‘British’),
(’’, ‘EU’, ‘rejects’, ‘German’, ‘call’, ‘to’, ‘boycott’, ‘British’, ‘lamb’),
(‘EU’, ‘rejects’, ‘German’, ‘call’, ‘to’, ‘boycott’, ‘British’, ‘lamb’, ‘.’),
(‘rejects’, ‘German’, ‘call’, ‘to’, ‘boycott’, ‘British’, ‘lamb’, ‘.’, ‘’),
(‘German’, ‘call’, ‘to’, ‘boycott’, ‘British’, ‘lamb’, ‘.’, ‘’, ‘’),
(‘call’, ‘to’, ‘boycott’, ‘British’, ‘lamb’, ‘.’, ‘’, ‘’, ‘’),
(‘to’, ‘boycott’, ‘British’, ‘lamb’, ‘.’, ‘’, ‘’, ‘’, ‘’)]