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tokens: allows for the simultaneous determination of Z g and Z ⋆ , tracing the ratio of oxygen to iron (O/Fe) in young stars and the surrounding ISM (Steidel et al. 2016 ). The O/Fe ratio is of interest because it is a sensitive probe of the star formation and chemical enrichment history of galaxies. Typical O/Fe ratios at high redshift are expected to be enhanced relative to the solar value due to the fact that the element abundance ratios in relatively young star-forming systems will be dominated by core-collapse supernova (CCSNe) yields (Maiolino Mannucci 2019 ). Indeed, this result has already been reported in the literature. Based on a simultaneous rest-frame FUV+optical analysis of 30 star-forming galaxies at z ≃ 2.4, Steidel et al. ( 2016 ) found O/Fe ≈ 4−5 × O/Fe ⊙ . Similar levels of O/Fe-enhancement have been reported for individual galaxies at z ≃ 2.3 in more recent studies (Topping et al. 2020a , b ). The observed O/Fe-enhancement (also referred to as α-enhancement) has a number of important implications. First, it places robust constraints on the typical star-formation histories at early cosmic epochs, confirming results from previous photometric analyses that the stellar populations at high redshift are typically 1 Gyr old (Reddy et al. 2012 ). Secondly, a deficit of Fe relative to O will mean that the stellar ionizing spectrum of typical high-redshift galaxies is harder at fixed oxygen abundance compared to galaxies in the local Universe. This relative hardening of the ionizing continuum at fixed O/H offers a natural explanation for the observed offset of z > 2 star-forming galaxies relative to z ≃ 0 galaxies in the common line ratio diagrams (e.g. the BPT diagram; Topping et al. 2020a ; Runco et al. 2021 ). Non-solar α/Fe ratios will also force us to re-think current stellar population techniques when applied to high-redshift galaxies. Almost universally, current stellar population synthesis models assume solar abundance ratios; accurate analyses of FUV-optical spectra at z > 6 with JWST will require new models allowing for non-solar abundance ratios. In this paper, we expand upon a number of previous works at z ≃ 2.5 (Steidel et al. 2016 ; Topping et al. 2020a , b ) and present a simultaneous analysis of FUV and optical spectra for a sample of 33 star-forming galaxies drawn from the VANDELS survey at z ≃ 3.4. Combining ultra-deep optical VIMOS/VANDELS spectroscopic observations (tracing the rest-frame FUV) with MOSFIRE H - and K -band near-IR follow-up (tracing the rest-frame optical), our analysis provides the first investigation of Z g and Z ⋆ for galaxies at z > 3, and we present the first estimates of O/Fe at these redshifts. In addition, we present both the stellar and gas-phase MZRs for our sample, tracing O/Fe as a function of stellar mass. The structure of this paper is as follows. In Section 2 , we discuss our combined VANDELS+MOSFIRE spectroscopic data set and describe our final z ≃ 3.4 galaxy sample (referred to