The proactive gain control hypothesis suggests that the global language context regulates lexical access to the bilinguals’ languages during reading. Specifically, with increasing exposure to non-target language cues, bilinguals adjust the lexical activation to allow non-target language access from the earliest word recognition stages. Using the invisible boundary paradigm, we examined the flow of lexical activation in 50 proficient Russian-English bilinguals reading in their native Russian while the language context shifted from a monolingual to a bilingual environment. We gradually introduced non-target language cues (the language of experimenter and fillers) while also manipulating the type of word previews (identical, code-switches, unrelated code-switches, pseudowords). The results revealed the facilitatory reading effects of code-switches but only in the later lexical processing stages and these effects were independent of the global language context manipulation. The results are discussed from the perspective of limitations imposed by script differences on bilingual language control flexibility.