After a secondary tense ἕως with the aorist optative sometimes in Attic prose implies an expectation, hope, or purpose on the part of the subject of the main verb that the action of the temporal clause may be attained. Since such optatives are due to the principle of indirect discourse, the subjunctive with ἄν, denoting mere futurity, might have been used instead.
σπονδᾱ̀ς ἐποιήσαντο ἕως ἀπαγγελθείη τὰ λεχθέντα they made a truce (which they hoped would last) until the terms should be announced H. 3.2.20 (here we might have had ἕως ἂν ἀπαγγελθῇ), τὰ ἄλλα χωρία εἶχον μένοντες ἕως σφίσι κᾱ̓κεῖνοι ποιήσειαν ( = ἂν ποιήσωσι) τὰ εἰρημένα they retained the other places, waiting until they (the Lacedaemonians) on their part should have performed for them (the Athenians) what had been agreed on 5.35. Compare ἕως ἂν ταῦτα διαπρᾱ́ξωνται φυλακὴν . . . κατέλιπε he left a garrison (to remain there) until they should settle these matters H. 5.3.25 (here ἕως διαπρᾱ́ξαιντο might have been used). Other examples are 13.25, 1.10, 7. 8 (ἕως οὗ?), H. 4.4.9, 27.5, 29. 43 (τέως), 33. 8; cp. also Eq. 133. Present optative in 3.102, H. 5.4.37.