How do I disable escaping when using COPY FROM in PostgreSQL?
The copy command by default uses text format with tab delimiter. So only one thing you need is to escape backslashes:

copy onegram (ngram, year, match_count, volume_count)
from program 'sed ''s/\\/\\\\/g'' &lt; /home/tims/data/ngram/test.tsv';
select * from onegram;
╔════╤════════════╤══════╤═════════════╤══════════════╗
║ id │   ngram    │ year │ match_count │ volume_count ║
╠════╪════════════╪══════╪═════════════╪══════════════╣
║  1 │ aX13_X     │ 2006 │           8 │            5 ║
║  2 │ aX13_X     │ 2007 │           4 │            3 ║
║  3 │ aX13_X     │ 2008 │           2 │            1 ║
║  4 │ a\         │ 1852 │           1 │            1 ║
║  5 │ a\         │ 1935 │           1 │            1 ║
║  6 │ a\         │ 1937 │           2 │            2 ║
║  7 │ ACT1V1T1ES │ 2003 │          15 │           11 ║
║  8 │ ACT1V1T1ES │ 2004 │          63 │            6 ║
║  9 │ ACT1V1T1ES │ 2005 │           1 │            1 ║
║ 10 │ ACT1V1T1ES │ 2006 │           5 │            4 ║
║ 11 │ ACT1V1T1ES │ 2008 │           4 │            3 ║
║ 12 │ ACTION="   │ 1995 │           3 │            3 ║
║ 13 │ ACTION="   │ 1996 │           6 │            5 ║
║ 14 │ ACTION="   │ 1997 │           9 │            7 ║
║ 15 │ ACTION="   │ 1998 │          19 │           11 ║
║ 16 │ ACTION="   │ 1999 │          11 │            5 ║
╚════╧════════════╧══════╧═════════════╧══════════════╝