In sonata form, development sections are characterized by tonal, textural, and phrase-structural instability. But are these instabilities counterbalanced by regularity in other musical domains? Are any syntactic layers more consistent in developments, relative to expositions or recapitulations? This corpus study examined hypermeter in expositions and developments from eighteenth- and nineteenth-century symphonic sonata movements. It analyzed both hypermetrical shifts (where a hypermeasure's duration differs from that of the preceding group) and hypermetrical deviations (where a hypermeasure departs from the four-measure norm). Developments had significantly less hypermetrical irregularity than expositions. This difference between formal sections was observed with all composers in the corpus, though they used varied amounts of hypermetrical regularity overall. These results, which are likely related to sequence blocks in the developmental core, suggest that hypermetrical grouping might serve a stabilizing function in sonata developments.