trial stage; experimental phase; prototype stage
Refers to a phase in development where a product, system, or plan is being tested or prototyped before finalization.
This device is still in the prototype stage; mass production will start next year.
Bugs are inevitable in software at the experimental phase.
試作品 is a tangible prototype or trial product, while 試作段階 refers to the stage or phase of trial production itself.
開発段階 is a broader development stage, whereas 試作段階 specifically emphasizes the trial or prototype sub-phase within development.
Compound of 試作 (trial manufacture, prototype) and 段階 (stage, phase).