Usually not, but decaf isn't caffeine-free. A typical cup still carries about 2 to 15mg of caffeine, versus 80 to 100mg in regular coffee, so one evening decaf is unlikely to wreck most people's sleep. The catch is dose and sensitivity: two or three decafs after dinner can add up to as much as a small regular coffee, and if you're a slow metabolizer or highly caffeine-sensitive, even small amounts can register overnight.
There's also a behavioral angle worth naming. A warm evening coffee — decaf or not — can become a cue your brain links with being alert and winding up rather than down, and the ritual itself can keep you sitting up later than you meant to. If decaf helps you cut back from regular coffee, it's a genuinely useful step; just treat the late cups with the same caution you'd give the real thing.
The Rest baseline still holds here: caffeine, including the trace amount in decaf, is best finished by 11am, or at least 8 hours before bed, if you know you're sensitive.
Full guide: Caffeine Cutoff: When to Stop for Better Sleep.
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