Basement floor hairline cracks

We recently had an addition built to our home which included a full basement space beneath. The floor was poured in September. Today I noticed several hairline cracks in the basement floor. Is this cause for concern? The entire project is nearing completion and I haven;'t yet gotten final inspections so there is a final payment I can withhold from my GC until this is resolved. Any light you can shed on this will be greatly appreciated. Thanks
TomL
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are their relief (expansion) grooves in the concrete? and did they install "wire" in the concrete?
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concrete on top of wire mesh on top of vapor barrier on top of gravel. no expansion joints.
TomL
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