The changes of the regime took place before the dissolution of the USSR and not followed after.

Andrei Sakharov was freed from exile by the personal order of Gorbachev in 1986. The article 70 of the Criminal Code of RSFSR (punishment for the Anti-Soviet activity) was repealed in 1988. The prison camp Perm-36 for political prisoners was closed entirely in the same year. By the major extent free elections to the Congress of People's Deputies of the USSR happened in 1989.

So by the moment when Russia declared its sovereignty and independence off the USSR in June 1990, de facto terminating the existence of the latter, little to none political prisoners were left in prisons.

"The War of Laws" between the Russian authorities lead by Yeltsin and the USSR authorities lead by Gorbachev lasted a year more, but compromise wasn't achieved and USSR technically ceased to exist in the next year.

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Edit: June, not July