Assange entered the embassy in 2012 to dodge a European arrest warrant issued over a Swedish probe into rape allegations, but Sweden dropped their investigation last year.
However, British police say they will still arrest Assange if he steps foot outside the embassy for failing to surrender to a court after violating bail terms.
Assange's lawyer Mark Summers told a London court that the warrant had "lost its purpose and its function".
Prosecutors are "expecting the decision today", according to a spokeswoman.
Ecuador earlier this month granted citizenship to Assange, who fears that if he leaves, he will be extradited to the United States over WikiLeaks' publication of leaked secret US military documents and diplomatic cables in 2010.
Ecuador also asked London to recognise Assange as a diplomat -- which would give him safe passage out of the embassy without fear of arrest -- but Britain refused.
Sweden dropped its investigation over the 2010 allegations last year. AFP